Juan, you should have no trouble being understood in the UK if you have a B2 certificate, but in my experience teaching in Spain, if you have the EOI certificate you probably haven't had a lot of opportunity to speak, and therefore might not be a confident speaker. You'll probably find that once you get to the UK you'll be fine. 

Are you planning to look for work? The difficulty might be that you struggle in a job interview. Practising the common questions employers ask, and making sure you know the vocabulary for your job would be very important before you go. Good luck.

Hey Juan Fernando,I am a British teacher of English.Maybe I can help you prepare.I think you will be able to understand my accent pretty well.