Jo Jackson beat Olympic gold medallist Rebecca Adlington to win the 400m freestyle in a new world record time at the British Swimming Championships in Sheffield on Monday. Jackson, 22, clocked 4 minutes 0.66 seconds, shaving 0.87 seconds off Federica Pellegrini's previous world mark set in 2008 European Championships. Adlington claimed the silver also in a record-breaking 4:00.89.

"Becky (Adlington) normally gets me on the last 25 meters and this time I thought to myself just kick and see what you can do," Jackson told British Swimming's website (www.britishswimming.org).

File photo of Jo Jackson

"I was in shock when I saw that time. It hasn't really sunk in yet." Victory for Jackson means she qualifies automatically for the 400m free at this year's World Swimming Championships in Rome while Adlington will have another chance to gain qualification for the event at the second trials in Scotland in June.

Adlington, 20, revealed that she had trouble with the pressure since claiming both 400m and 800m titles as well as a new 800m world record at last year's Olympics in Beijing.

"My motivation is never a question, it's how to deal with the pressure," she said, "Not even my mom and dad can teach me how to cope with the pressure."