As long as all stakes are returned as prizes there is no limit on the value of stakes or the size of prizes.
However the retention of any stake money (e.g. as a way of raising funds to support the aims of the club) would be in contravention of the exemption which applies to clubs with more than 25 members (established for purposes other than gaming) under the Gaming Act 1968. (If some of the stake money is retained the club would need to be registered in the same way that, say, Mecca Bingo is).
Chris