Olympic 800m silver medallist Keely Hodgkinson ran a personal best to break the England U23 Championship record and win the 400m title in Chelmsford.
The 21-year-old triumphed in 52.24 seconds to better Christine Ohuruogo’s mark of 52.43 from 2005.
Hodgkinson, whose previous best of 52.41 came last year, dropped down to the 400m in Essex from her usual 800m.
“Deep down I wanted a bit of a faster time. I was hoping for a 51,” she told England Athletics.
“I feel that is what I am capable of, but it was very windy and it was a straight final.
“It’s a new, new experience doing a different event in a championship environment with girls who can push me.”
Natasha Harrison finished second and Poppy Malik third.
Hodgkinson set a world indoor 600m record of 83.41 in Manchester in January and broke the British 800m record of 1:55.77 at last week’s Paris Diamond League meeting.
The two-day U23 Championships end on Sunday.