Yes, flying a tug to stay current sounds nice doesn't it? Except you will have to fly it often enough to stay current at doing that, and depending on the club they might want to put you on a rota. I imagine you would be asked to join the club as well, for a variety of reasons including insurance. So, it isn't free flying.
You have the information on the BGA website (all 57 pages of it!), if you are still interested your next move in my view is to go to your nearest club and start talking.