Basketball's not big at all in England, although Lual Deng profile is slowly changing that.
I went to see the London team from the BBL (British Basketball League) play about 6 months, crowd was probably no more than 400 or so, more than you'd get at your average ABL game but far less than what you'd see in the NBL.
The standard of the game was like the crowds, somewhere between ABL and NBL. They don't seem to have the same import restriction rules we have in the NBL as I'm pretty sure one of the teams was fielding at least 4 players from the States. About 2 years ago Dennis Rodman played one or 2 games for one of the team (Brighton?) and that generated a lot of publicity and filled the stands, FWIW he didn't do much in the stats column but I'm not sure this is neccessarily indicitive of the standard of the league.
The most annoying thing about the game I went to was the fact the MC was commentating through the ENTIRE GAME as though we were listening on radio and not actually there seeing things unfold "Smith dribbles down the court, passes to Jones on the wing....". It was genuinely terrible, made worse by his London ghetto accent and the fact he clearly didn't know much about the game.
I did manage to score the prize in the 50/50 raffle, a lazy 20 pounds for my troubles (they sold a wopping 40 tickets!) so that more than covered the entrance fee which from memory was around 8 pounds (AU$20).
(Mod: Informative - cheers.)