I went through a bit of this - basically, having taken your exams, you shouldn't have to take them again - just pay the money to renew. Your IR needs a retake with the CAA after you have gone more than five years past the last expiry without renewing it (it expires every 12 months) - the same goes for type ratings, except substitute currency for expiry - otherwise, you can just get it renewed with your local friendly IRE.
Mind you, they do change the rules, so check again.
Phil