Happens to me all the time, Ive been stopped around estates with friends alot, Most of the time, its due to us looking dodgy, Im not a dodgy person, but the clothes in which you wear ( hoody, cap ) makes them stop you. I got searched once for god sake, also, I was in a crowd one time, and a couple of police officers stopped us, and said that the crowd we were in had to seperate, they said that a large crowd of people may intimidate others around you.
I also got questioned for a robbery that went on, I was let go as I wasnt the person, but it ticks me off