As someone who has been on the receiving end of a HMRC audit it’s not nice.
3 years worth of accounts, access to bank statements for those 3 years, payment providers I used, in fact I was so open I felt like I’d been felched by a velociraptor (quick dinosaur reference for the kids).
Anyway I had been doing my own accounts working from home, all was ok apart from I’d made the schoolboy error of offsetting my entire mortgage against my income. This was a little naughty and I ended up having to pay back £3k in back taxes and sharpish.
On the plus side I avoided the HMRC penalty of 100% fine of tax owed due to coming clean and having a little sob. IIRC I got hit with 10%.
N.B. The fine can be up to 200% if your well dodgy.
To be fair my tax inspector was gorgeous.
Anyway the wheels of the HMRC may turn slowly but they do turn, some will get away with it some won’t.