In early August 2026, HMRC confirmed it is again contacting individuals it believes may have underpaid Income Tax or Capital Gains Tax on cryptoasset activity. If a letter arrives from HMRC referring to your crypto, it is not random, it is not a general mailshot, and it is not something to file away and think about in January.
It is also not an accusation, and it is not an investigation. What it is, is an opportunity with a deadline attached, and the value of that opportunity falls sharply the longer you leave it.
This article explains what these letters are, why the campaign has escalated so steeply, the single distinction that determines how much a mistake costs you, and what to do in both situations: when a letter has arrived, and when it has not but you know your records have a gap.
What a nudge letter actually is
A nudge letter is a targeted prompt. HMRC sends it to a taxpayer whose data suggests activity that does not reconcile with what has been declared, and invites them to review their position and correct it.
Three things it is not, and confusing them causes bad decisions:
It is not a formal enquiry. HMRC has not opened an investigation into your return. There are no statutory information powers being exercised, and the letter does not by itself extend or restart any time limit.
It is not an assessment. HMRC is not telling you that you owe a specific amount. In most cases the letter does not name a figure at all, because HMRC's data shows activity rather than a computed liability. Gross disposal proceeds reported by a platform tell HMRC nothing about your acquisition costs.
It is not proof that you have done something wrong. Data matching produces false positives. Someone who traded actively but at an overall loss can look identical, in the data HMRC holds, to someone who made substantial undeclared gains. That does not make the letter safe to ignore, but it does mean that the correct first step is to compute your actual position rather than to assume the worst and confess to it.
What the letter does do is start a clock, and change your status in a way that has a direct financial consequence.
The numbers behind the campaign
The escalation is easier to understand with the figures in front of you.
For the 2024/25 tax year, HMRC sent approximately 65,000 nudge letters to crypto investors. The year before, the figure was 27,700. That is more than double in a single year, and the data came out through freedom of information requests rather than a public announcement.
Set against that, the recovery figures are modest. HMRC has recovered around £8.3 million from 502 investors across two years through crypto tax settlements. That is an average settlement in the low tens of thousands, from a very small number of people relative to the letters sent.
Read those two sets of numbers together and the strategy is clear. This is not an enforcement operation working through cases one at a time. It is a volume prompt designed to move a large population towards voluntary correction cheaply, before the data arrives that would make case-by-case enforcement practical.
Commentators have made the point that HMRC's reliance on nudge campaigns partly reflects how difficult this area is to police directly: existing tax provisions map awkwardly onto cryptoassets, and HMRC's own technical understanding is still developing. A prompt that asks the taxpayer to do the work is cheaper than an enquiry in which HMRC has to do it.
That balance changes in 2027.
Why HMRC's targeting is getting sharper
The letters are better aimed than they were, because the inputs are better.
Exchange data on request. HMRC has obtained customer data from UK-facing exchanges for years, including historic bulk requests covering users above certain transaction thresholds.
Domestic reporting from 1 January 2026. Separate UK reporting obligations took effect at the start of 2026, expanding what HMRC receives without having to ask.
Blockchain analytics. On-chain analysis links wallet activity to identities established at the exchange layer. A withdrawal to self-custody does not sever the connection; it records it.
CARF from 1 January 2026. This is the one that changes the picture structurally. UK cryptoasset service providers are collecting verified identity and transaction data on their users, with the first reports due to HMRC by 31 May 2027, covering calendar year 2026. International exchange between participating jurisdictions follows later that year, which means platforms outside the UK feed the same system through their own regulators.
The practical implication is that the current campaign is the last one that runs on partial data. From mid 2027, HMRC will hold a structured, standardised record of what UK residents did on platforms during 2026, and further campaigns will be built from it.
You invest. We take care of the fiscality.
The distinction that decides the cost: prompted or unprompted
If you take one thing from this article, take this.
UK penalties for an inaccuracy depend on two variables: the behaviour behind it, and whether the disclosure was unprompted or prompted.
A disclosure is unprompted when you come forward at a time when you had no reason to believe HMRC had discovered, or was about to discover, the issue. It is prompted when you come forward after HMRC has already made contact.
A nudge letter converts one into the other. Correct your position before the letter arrives and you are in the unprompted range. Correct it afterwards and you are in the prompted range, for the same mistake, on the same facts.
The standard penalty ranges, as percentages of the tax understated, illustrate the gap:
Careless error, unprompted: 0% to 30%
Careless error, prompted: 15% to 30%
Deliberate, unprompted: 20% to 70%
Deliberate, prompted: 35% to 70%
Deliberate and concealed, unprompted: 30% to 100%
Deliberate and concealed, prompted: 50% to 100%
Note the bottom of the careless unprompted range. It is zero. Where the error was careless rather than deliberate and the disclosure is unprompted and of good quality, the penalty can be reduced to nothing. That outcome is not available once a letter has landed.
Where the position falls within each range depends on the quality of your disclosure, assessed under three headings HMRC calls telling, helping and giving access: how fully you explain what went wrong, how much of the work you do rather than making HMRC do it, and how readily you provide records. Complete, well-documented figures are not just good practice; they move you to the bottom of the applicable band.
Two further points:
Penalties can be higher again where offshore matters are involved, which for crypto is a live question given how many platforms are established outside the UK; and
Interest runs separately from penalties, charged from the date the tax was originally due, at a rate that tracks the Bank of England base rate.
If a letter has arrived
Read the deadline on the letter itself. These campaigns vary, with response windows commonly in the 30 to 60 day range. The letter states its own; do not rely on what you read in a forum.
Do not ignore it. Non-response does not make the matter go away. It removes the cheapest route out of it and makes a formal enquiry considerably more likely.
Do not respond immediately either. The worst two responses are silence and a hurried reply built on estimates. A letter that says you owe nothing, sent before you have computed your position, is a statement you may have to withdraw. Use the window to establish what is actually true.
Compute your real position first. Pull complete transaction histories from every exchange, wallet and protocol you have used, for every year in scope. Value each disposal in sterling at the transaction date. Apply the UK matching rules: same day first, then the 30 day rule, then the section 104 pool. Identify income events separately and value them at the date of receipt.
Establish whether there is actually a shortfall. There may not be. Active trading generates enormous gross proceeds while producing modest or negative net gains, and gross proceeds are frequently what triggered the letter. Equally, you may find you crossed the £50,000 total disposal proceeds threshold, which requires you to complete the capital gains pages even where the gains themselves are small or nil.
Then respond, on the basis of numbers you can evidence. If there is nothing to correct, say so and be able to show your working. If there is, correct it through the appropriate route.
Get advice where the amounts are material or the behaviour question is live. The difference between careless and deliberate is not a technical footnote. It changes the penalty range, and it changes how far back HMRC can go.
If no letter has arrived, but you know there is a gap
This is the more valuable position to be in, and most people in it do not realise how time-limited the advantage is.
HMRC operates a dedicated Cryptoasset Disclosure Service, accessible online through a Government Gateway account. It is designed for exactly this situation: you tell HMRC which years are affected and what the correct figures are, and you pay the tax, interest and any penalty.
Coming forward through it before any contact from HMRC is an unprompted disclosure. As set out above, for a careless error that can mean no penalty at all.
Weigh that against the calendar. The 2026 calendar year is being reported to HMRC by 31 May 2027. Every month between now and then is a month in which unprompted disclosure remains available. After the data arrives and is worked through, the window for a large number of people closes, and it closes without warning.
How far back does this go? The assessment time limits depend on behaviour. Broadly, four years where reasonable care was taken, six years for carelessness, and up to twenty years where the inaccuracy was deliberate. Offshore matters can extend the period further. That range is why the behaviour question matters as much as the arithmetic.
Why so many of these errors are genuine
It is worth saying plainly that most crypto under-reporting is not evasion. The UK rules produce taxable events in places that are counter-intuitive to anyone who has not read the guidance, and the same handful of mistakes recur.
Crypto to crypto swaps. Trading ETH for SOL is a disposal of the ETH at its sterling market value, even though no pounds moved. People who never converted to fiat routinely believe they never triggered anything.
Staking, mining and airdrop income. These are usually taxed as income at the sterling value on the date received, not when sold, and not when withdrawn. Rewards left sitting on a platform are still taxed.
The matching rules. UK disposals are matched same day, then 30 day, then against the section 104 pool at average cost. Anyone applying FIFO out of habit from another jurisdiction's rules will produce wrong numbers even with complete records.
DeFi deposits. Under HMRC's current interpretation, transferring tokens into a lending protocol or liquidity pool can be a disposal at that moment, because beneficial ownership passes. This is the change that the no gain, no loss reform will address from 6 April 2027, but that reform does not reach backwards. Historic deposits stay under the existing analysis.
The £50,000 proceeds threshold. The capital gains pages must be completed where total disposal proceeds exceed £50,000, regardless of whether the gains are small. Active traders cross this without noticing.
Wallet transfers. Moving your own coins between your own wallets is not a disposal, and over-reporting these is as common an error as under-reporting the real ones.
Since 2024/25, the Self Assessment return has had a dedicated cryptoasset section within the SA108 capital gains pages, which removes the old excuse that there was nowhere obvious to put the figures. It also makes an omission more visible, in both directions.
What the April 2027 reforms do and do not do here
There has been a lot of coverage of the July 2026 announcements, and some of it has produced exactly the wrong conclusion for anyone in this situation.
From 6 April 2027, subject to the Finance Bill process, qualifying cryptoasset lending and liquidity pool arrangements get no gain, no loss treatment, and eligible stablecoins become exempt from Capital Gains Tax for individuals and trustees.
Neither measure is retrospective. Neither one forgives a historic position. A DeFi deposit made in 2024 remains analysed under the rules in force in 2024, and a stablecoin swap made in 2025 remains a chargeable disposal.
If anything, the reforms sharpen the point rather than softening it. The years currently in scope for nudge letters and for CARF reporting are precisely the years that run under the old, harsher rules. The relief arrives after the data does.
A short checklist
Establish which tax years are potentially affected.
Pull complete histories from every platform and wallet, including ones you no longer use. Platforms exit markets, and their data leaves with them.
Value every disposal and every income event in sterling on the correct date.
Apply same day, 30 day and section 104 matching, not FIFO.
Separate income events from capital events before computing anything.
Check the £50,000 proceeds threshold for each year, not just the gains.
Identify whether any shortfall arose from reasonable care, carelessness, or something more.
If no letter has arrived and there is a shortfall, use the Cryptoasset Disclosure Service while the disclosure is still unprompted.
If a letter has arrived, respond within its stated window, with figures you can evidence.
Keep the underlying records. HMRC expects records supporting a return to be kept for at least five years after the filing deadline, and a disclosure covering earlier years needs the evidence behind it.
Where Finbooks fits
Every route out of this situation runs through the same bottleneck: a complete, correctly valued, correctly matched transaction history, often covering years you were not tracking carefully at the time.
That is not a tax problem in the first instance. It is a reconstruction problem. The tax analysis is straightforward once the data exists, and close to impossible when it does not.
Finbooks exists to do that reconstruction. Pulling activity together from exchange APIs, CSV exports and on-chain wallet addresses across chains and protocols. Valuing every disposal and every income event in sterling on the correct date. Applying the UK's own matching order rather than a generic one. Producing figures for the SA100 income entries and the SA108 capital gains pages, with the schedules kept behind them so a number can be explained rather than merely asserted. Start today reconstructing your crypto tax history with the 7 days free trial.
