Leander ended up as national champions, with Mount Kelly, who had qualified for the final fastest, taking second at Ponds Forge. Third place went to Hatfield.
Plymouth Leander’s quartet of Reece Dunn, James Watson, Freddy Clampett and Tom Fannon touched in 3:25.58.
Mount Kelly’s team of Sam Dailley, Harry Noble, Alessandro Burdisso and Federico Burdisso clocked 3:27.34, which was a new club record, with Hatfield finishing in 3:33.90.
Mount Kelly’s Italian 16-year-old international Federico Burdisso did produce an impressive last leg, clocking 49.80. He was the only swimmer to produce a sub-50 second split. Plymouth’s Fannon had the second fastest split with 50.30.
Leander’s Laura Stephens and Jessica Jackson both reached A finals for the second night running.
Stephens, who had won the national 100m butterfly title on Wednesday evening, finished eighth overall and sixth Brit in the 100m backstroke with a time of 1:02.96, while Jackson came seventh overall and fifth Brit in the 50m freestyle in 25.81.
Leander’s Tegan Drew and Mount Kelly’s Athena Clayson both reached the 100m backstroke B final, with Drew clocking 1:03.31 to finish fourth and Clayson touching in 1:03.45 for fifth.
Leander’s Juliette Casini reached the B 50m freestyle final clocking 26.70.
There were also B finals for Mount Kelly’s Federico Burdisso and Oliver Traverner and Leander’s Marcus Gardiner and Adam Chillingworth.
Gardiner clocked 1:04.26 to finish third in the 100m breaststroke final, with Chillingworth coming sixth in 1:04.61 and Travener 10th in 1:05.26.
In the morning’s heats of the 100m breaststroke there was an stunning swim from Dartmoor Darts’ 13-year-old Cameron Williams.
Williams clocked 1:07.55 to break the British Age Group record by an impressive 0.43 seconds.
Afterwards his coach Matt Henry said: “It feels amazing. It’s such a great achievement. I’m really proud of Cameron. It’s fantastic when something you both work towards comes together.”
Federico Burdisso finished fifth in the B 200m freestyle final in 1:53.36.