Gym membership is an expensive pastime, with a typical monthly fee being at least £50. But unless you go at least 3 times are week you are unlikely to be getting good value for money.
If you are an infrequent gym user (you may do other sports activities as part of your fitness regime) or just want to get into going to the gym before you commit to a long term contract then there is a a website that can provide flexible discounted pay-as-you-gym visits.
Payasugym.com allows you to get pay-as-you-go one-off passes to hundreds of gyms which may work out cheaper than the usual gym membership. There are no inductions and you only pay for what you use. Simply search their database for a gym near you then buy the gym pass that suits and away you go.
If you are looking for a fun and free way to work out have a look at http://www.facebook.com/Free24FITClub. Completely free, great trainers and opening up all over the UK!