I'm a BSAC Instructor so obviously a little biased, it's a good cheap way to learn/improve your diving, the Instuctor route is extremely good value, but you do it for free so no income from nice dive spots abroad. I also have TDI quals so I'm not exclusively BSAC
I don't think I can add anything more to the constructive comments made by others above, except here's a url to find a local branch if you wanna go BSAC. I'd advise checking out the club memberbase before committing, some clubs are full of nice people, some are run by a bunch of ****s. Membership fees for BSAC are fixed (think yours would be £37.50 per annum, membership fees for the actual branch vary a great deal as does what you can expect for your money. The skill development courses are also very very reasonable .
HTH
Steve
http://www.bsac.org/branches/branchlist.htm