Cheltenham and Liverpool Lizards have won the British Water Polo League men's and women's titles respectively.
Cheltenham beat Lancaster 14-13 in a thrilling final game of the season on Sunday in Surrey.
Both sides had gone into the match knowing that a win would be enough for them to take the title.
Liverpool sealed the women's league on Saturday with victory in their penultimate match and finished their Super 5s campaign with a 100% record.
|Women's Super 5s 2014-15|
|City of Manchester||8||5||0||3||+33||10|
|City of Coventry||8||5||0||3||+14||10|
"This is the culmination of five years' hard work," Liverpool Lizards head coach Gordon Dacre told BBC Sport.
"The difference this year is that all our international players have come back to play with the squad. Their overall fitness has made a big difference."
Great Britain and Liverpool captain Rosie Morris added: "There have been a few close games but we wanted to try and win every game rather than take any gloss off of winning the league."
Liverpool also won last year's British Championships, beating London Otter 15-12 in the final.
"We had that base last year and we've built on it this year," Great Britain and Liverpool defender Fiona McCann added. "The younger players have really stepped up this season."
While the destination of the women's title was known before the final day of fixtures, the men's title was not decided until the last few seconds of the season.
|Men's Super 5s 2014-15|
|City of Manchester||8||2||0||6||6||4|
Cheltenham led by no more than one goal for the majority of the game thanks, in part, to four from Great Britain's Rob Parker.
Having trailed by three goals at the start of the final quarter, Lancaster fought back to level the game at 13-13, before Cheltenham's Adam Legge scored a dramatic late winner.
"I'm exhausted," Cheltenham coach James Ross said. "It was nail-biting stuff but I think we were in control of the game most of the time."
Parker added: "We have come right the way through from juniors and it's such a tight-knit team - I think that's probably the key.
"We'll hopefully take this into the national championships and get the double."
Lancaster head coach Zak Sly, whose side finished third last season, said: "We went in as the underdogs but we kept fighting back.
"It was really close but we knew we had to win, a draw wasn't enough."
Cheltenham hope to defend their British Championships crown at this year's finals in Lancaster in May.