I'm in North London, and I joined our local leisure centre. It costs approx 40/month. The nice thing about the membership is that there are no contracts, so I can quit whenever I need to. The facilities are perfectly decent (not amazing, but totally fine for my needs). There is a pool in this facility (which I have yet to use) and I also have use of the other leisure centres in the council which have tennis courts and a full range of classes which are free with my membership.
I really like my gym. It's a nice mix of people (all different ages and fitness levels). When I joined I was assigned a trainer (for free!) who designed a program for me, and met with me once a week for my first month or so. I can make free appointments with him whenever I feel I need a change to my program, or just need some motivation. I know in my gym in NYC any personal training was an extra (and large!) cost, so I feel that this is a pretty good deal.
At the end of the day, the leisure centre isn't that much cheaper than Fitness First, but I went with them because it was a much friendlier environment, without the pushy hard-sell sales reps that I encountered at FF.