I was in a band and they all got a a ltter from HMRC demanding £4k each.
Spoke to guitarist from his new home sat on the bog, terrified.
Drummer sorted us all out. He had an accountant for his self employed stuff that he added the band to.
I used to send in a spreadsheet of earnings, mileage, phone calls, stage clothes, repairs, set-ups,
equipment costs, depreciation, etc etc etc. Had rebate on day job tax a few times.