Fantastic. List of "Sources of data used" confirms they're doing what I'd hope they were doing.

Nearest encounter I've had with this sort of thing was a relative's account of some antics of their social circle involving attempts to claim their address was somewhere that'd get them into the catchment area of popular schools. Local authorities are well aware of every trick in the book of course, and easily send people away with a flea in their ear (amusingly, the "we don't believe you" letters were signed by a "Ms. Snooper". Which has *got* to be someone having a laugh, surely.) It seems to me that most people seriously underestimate how much of a paper/digital trail they leave out in the world, for anyone granted a bit of authority to access it. (Mind you, there used to be stories like https://www.theguardian....localgovernment.ukcrime ).

Use of AI may yet get interesting/controversial. "Computer says you're probably guilty, but it can't say exactly why or what of. So we'll just treat you as being guilty...". And so welcome to Kafka-world.

To be absolutely clear (as you request), I don't know and do not think that anyone could answer that.
I think it very unlikely, but realistically, you're on your own!

Your Capital Gains Summary in your Tax Return report will not show rental income, by the way; the details requested are disposal proceeds, allowable costs (which include the purchase price), and total gains in the current year on this transaction.
No date of purchase is required.

The CGT summary is SA 108, and here it is on the HMRC website:
https://assets.publishin...8_English_Form_2021.pdf

I am not so sad as to know this all by heart - I disposed of a let property last year.

I know of someone who did this for 20 years - HMRC caught up with them & it nearly ruined them - HMRC would NOT let them off (quite right) - in the end they borrowed from siblings against a future inheritance -- but HMRC have long tendrils and this chappie had better be honest and own up quickly - thats a plus point at the start.

People are fools thinking they dont have to pay tax !

There is a rush to judgement here which may well not be fully deserved.

Its perfectly possible for situations to arise where no tax actually falls due.

Take gross rents, less interest only mortgage (where repayments are the same as the interest), less repairs and renewals through year, less agents fees, less accountant's tax return prep fees.

And then, if there is a small profit, perhaps he has no other income from other sources year on year? Or perhaps just some of the years in question? His overall income may have been lower than the personal allowance for that year.

Or perhaps he has opening years losses from a trade that can be set against other income. Or, perhaps cessation losses that can be set against other income (Year on year trading losses couldn't be though...)

I'm just trying to illustrate that there are so many variables. That's why sitting down with an accountant first up, establishing the exact position, is the crucial first step. Once you know the potential liability, then you can look at the interest/penalty position. And then, you formulate how you will approach HMRC.