Southend is the obvious place. It's H24 - but beware the "after hours" supplement (I think it's after 10pm, but I'm not sure). The flying schools there all know about it, and will avoid you getting caught.
There are several clubs at Southend - Seawing, WillowAir, Southend Flying Club, and more. I know quite a few of the instructors - there are a goodly crop who have been instructing for decades, aren't "hours builders" , and will look after you.