Wow, that's not bad at all!
I currently pay £35.00 for my Gym membership at a local council-run gym.
When I went to Cannons two years ago I was paying around £47 a month so I guess it would be higher now.
My quote for the health insurance was between £34.37 and £51.75 per month
From how I read it, you pay an "activation" fee of £25, then pay £25 a month for three months (based on Cannons) and then if you go twice a week or more, you get it for free.
I also like how you will have to start paying for the membership fee if you stop going for twice a week, however do they take into consideration holidays, you can't go if you're abroad can you? do they average it up over the month or something?
Also if you sign up through this link:
Quidco - Pru Health you get £85 cash back, which is almost the cost of the 'activation fee' and three months fees.