France is not Sweden (yet), most people would not see finding nearly 500 euros that they didn't know about as a "problem".
If the British coins are the old round unimetallic type then they are a problem, as there is no government institution where you can exchange them and commercial banks will only exchange them for account holders.
I was just about to ask about that.... I have two kinds of one Pound coins.... some old and some new... I guess the easiest thing to do will be to give them to my friend who lives in the UK?