You need tax help from an accountant priddy quig
quite honestly
My (late) Mother had one of those heralding real trouble over a period of years. Over 80 ( no not over a length of time of 80 y ) she had been doing her own accounts and had rather lost it - and the tax man had Noticed.
We had to hire an acct and then a tax lawyer to fight the case. Final tax bill after 24 mo was £1,000, but lots and lots of time and substantial fees to the lawyer - and of course since we paid unpaid tax, we couldnt squawk about victimisation of little old ladies....