Fran Halsall registered the fastest 100m freestyle time of 2011 with a swim of 53.61 seconds at the ASA National Championships in Sheffield.
The 21-year-old's time edged out the Netherlands' Fenke Heerskerk at the top of the world rankings.
Halsall, whose previous best for the season was 55.01, finished two body lengths clear of her nearest rival.
She will not swim in Wednesday's final having already qualified for July's World Championships in Shanghai.
Halsall, who will concentrate on freestyle in China after being edged out in the butterfly on Monday, will hope to improve on her 2009 world silver medal.