Thanks for the speedy replies chaps, some good advice received. Certainly putting my mind at rest somewhat.
Good advice given. I used to put 20% a month by direct debit into a savings account, which covered my tax and NI. I was advised by my accountant (since 1992) to staple my invoices with the receipts for that period in an A4 book. At the end of the year i take my book to him (he used to work for 9 years inland revenue prior 1992) and he sorts everything out for under £200. My accountant is a ST holder as well.....