To compete in some of the competitions it is necessary to be a British Gymnastics member. There are many other benefits too, the most important of which is Insurance cover against any accidents.
In order to become a member follow this link below.
If your tumbler is competing in Club 1, 2, 3 or 4 then the membership they need is 'Gymnast'.Â
If they are competing at Club 5 or above they need to have the type 'Competitive Gymnast'
The club you are looking for is Team Treasure not one of the other Winchester clubs.
Here's the link:
British Gymnastics Membership
(Scroll down the first page to find out more information)