It's probably legal and in their terms and conditions, but if you go to a single event, they will actually sign you up for a recurring monthly bill of £24.99. They are a disgustingly sneaky in this and you probably wont get your money back, but definitely drop them immediately.
Tip for consumers: Log in to your account and make sure you are not signed up for a recurring membership charge. It is NOT explicit... If you have a 'platinum' membership, then you WILL be charged after the 'free' trail month.