Have a look here
You can get your ICC by doing the RYA Powerboat Level 2 course and then sending a photo and some dosh to the RYA (but it's cheaper to join the RYA - then you get the ICC free!). You can buy a book (The RYA Book of EuroRegs for Inland Waterways by Marian Martin) to learn all you need to know for the CEVNI test, which is a short multiple choice test which you can take during your PB2 if you let your instructor know in advance. CEVNI is only needed if you will be using the inland waterways of the continent. HTH!