My friend has recently convinced me to start going to the gym with him. I didn't want to sign up for a contract for 12 months and then have to keep paying monthly if I decided I didn't want to go.
After looking on google, I came across a website called MoveGB.com. It is basically a "Portable" gym membership which allows you to use lots of local gyms in your area (a lot of them are free with the membership, some are discounted rates).
They currently are doing an offer where you can have a 10 day free membership (if you don't like it there is an option under My Account to cancel it, although I haven't tested this yet due to mine still being active).
I haven't had any problems using it at 2 of my local gym's.
With the membership I think you can also attend boot camp sessions and fitness classes.
They do various membership plans but for £10.49/wk you can use lots of gyms for free. Although that's £41.96 a month, you are not restricted to one gym and you also have the classes included. But the main thing for me is that I can cancel the membership, if I don't want to go anymore.
Hopefully this will be helpful for others...
Check which gyms are available in your area here: https://www.movegb.com/all