World Silver Medallist Hannah Miley followed suit in the same event for the women, also posting the fastest time in the world for the 400m Individual Medley.
Despite a fast start from Middlesborough's Aimee Wilmott who led out for the first 100m, Miley kept her cool and with just three lengths to go, was just outside her British Record.
Finishing strongly in 4.32.67, Miley posted the second fastest time in British history to take the title in an Olympic qualifying time.
"The performance was really good," Miley said. "I did not expect the time nd I am really chuffed. The crowd was electric and I can't wait to see what it will be like at the Olympic Games.
"The pressure is off now I have qualified. Training has been great, now I have to maintain it. In the past at major sport competitions I train well then I go out and let it drop, so I now need to maintain it."
Wilmott, who followed Miley's heels posted a personal best of 4.37.48 to take silver within the qualifying time.
Steph Proud took third place and the bronze medal in 4.43.10.
Ellen Gandy set up a gladiatorial final after posting a personal best of 57.47 in the 100m butterfly semi-final.
In what promises to be one of the closest races of the week, Gandy edged out Fran Halsall to the fastest qualifier spot after Halsall also won her semi in 58.31.
Jemma Lowe was close behind to finish in 58.79 securing her a spot in tomorrow's final. Competition for the top two spots will be in close contention with Jessica Sylvester, Rachael Kelly and Sophie Allen and Jess Dickons also finishing in under a minute.