I'm a self-employed freelance consultant. I issue invoices and receipts for all work I do, and retain hard and digital copies, plus a handy Excel tallysheet. I run work payments through a business bank account (might I recommend Bank of Scotland since they do a free account - most business accounts levy charges on you), and pay myself a salary (minus 33% for NI, Tax and other bits 'n bobs that might arise) into my personal account. I'm registered as self-employed and at the end of the tax year self-assess myself based on the excel sheet and invoices. I can (obviously) supply copies when requested to the Inland Revenue.