Yes, you must provide an accountants certicate confirming the unaudited accounts if you are a sole trader. Unfortunately UKBA have retained my documents so I can't show the format of what mine looked like.

Basically it was a letter showing my gross and net earnings for the year with a signed statement from a suitably qualified accountant at the bottom, stating that based on the accounts I had given to him, he confirmed the amounts shown. I also signed it to say that I accepted his confirmation.

My accounts are very simple, all paperwork was in order. He charged 100 pounds for this.