We do not maintain a database of all polo clubs on the website but Swim England, water polo’s governing body in England, can provide you with the info you need. We recommend you try this link > https://www.swimming.org/waterpolo/finding-english-water-polo-clubs/
University water polo competitions in the UK are provided by 2 organisations...

Great Britain finished their World Cup Division Two campaign on a high with a hard-fought 13-12 (3-4, 3-1, 6-3, 1-4) victory over Portugal on Sunday afternoon in Malta. Theo Nousios’ squad took control after the first quarter, but had to dig deep in the fourth to secure seventh place overall, as the Portuguese fought back to level late on. Izzy Howe was the hero, sending in an exquisite lob shot with 1:07 remaining to win the game.