It's mainly just their approach to crypto taxation which meant I had to go back through 3 years of exchanges and declare income/capital gains. Since I use coinbase, HMRC have got all UK customer info from them so had to use Koinly to calculate everything.

When I called them up, they said all they need is a handwritten letter with declaration on, so I busted out the Parker Fountain pen ✒ 😁 However, that's all sorted now and am back in action.