mg, what level are you talking about?
i recently converted my faa ppl to jaa so i can tell you about that
you need to be up & current on your hours (pref 12 in the last year)
written exams which consist of air law and hpl (£30 each)- you will also need a uk rt licence (£50)
then it's a full skills test sadly
but if your refering to cpl / atpl afraid i can't help