In reply to benedetta7277:
Best bet would be to join one of the London based clubs [LMC for example]. Since you have already climbed, it would be relatively simple to come along to one of their meets and get climbing.
Only possible difference is that in the UK there's a minority of sport climbing, which I'm guessing is what you're used to coming from Italy? - majority of outdoor routes are trad.
In terms of actual venues, you have the southern sandstone (reachable by train from London in under 2 hours), and then about the nearest would probably be Cornwall or Wales. So in other words - indoor is all you're gonna get unless you drive for 4-5 hours.
Hope that helps