The 22-year-old Olympic bronze medalist finished in 4 minutes, 00.66 seconds, lowering Federica Pellegrini's mark by almost a second. Pellegrini swam 4:01.53 at an Italian meet earlier this month.
"To get a world record has just blown me away and for Becky to go under the world record as well, I'm so happy,'' Jackson said."I knew it was going to be so tough coming here because Becky is swimming amazing. She really pushed me there, I wanted it so much.
"I've never had the British record in the 400, so it's my first British record in the 400 and the world record. It's not a bad one.''
Two-time Olympic champion Rebecca Adlington finished second, also under the old mark, touching in 4:00.89.
"I'm a just turned 20-year-old girl and to deal with the amount of pressure and expectation on me has been harder than I've ever thought,'' Adlington said. "No one can prepare me for that, not even my mum and dad, so I've just had to deal with it as best as I can and hopefully that race showed I have dealt with it quite well.''
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