Jo Jackson and Lizzie Simmonds both qualified for next month's World Championships in Shanghai but Fran Halsall found herself being pipped by Jemma Lowe on the first night of finals at the British Gas ASA National Championships in Sheffield.

Jackson, of Richmond, produced a powerful swim in the 200metres freestyle while Simmonds was a clear winner in the 100m backstroke as both swimmers responded to the disappointment of not qualifying at the first trials in Manchester in March.

Halsall led from the start of the 100m butterfly to the final stroke where she was edged out by 0.01secs by Lowe, who hails from Hartlepool.

Jackson, the Olympic 400m freestyle bronze medallist, produced her fastest time for two years as she held off the challenge of former double Commonwealth champion Caitlin McClatchey to touch in one minute 58.32 seconds.

For 18 months ill health and asthma so severe her ribs popped out in training have blighted Jackson's career after her triple medal-winning exertions in Rome in 2009.

Jackson said: ‘‘It's such a relief. I wanted to go quicker tonight but to get the qualifying time and book my spot for Worlds, I can't explain how happy I am.

‘‘This time last year I didn't think it would happen so I am so relieved and that is what the smile is for.

‘‘It has been really hard but I put in a lot of effort these last few months changing so much and it's definitely starting to pay off.

‘‘I still think there is more there and me and (coach) Ben are going to go away and work on different things.''

The strength in depth also bodes well for the 4x200m relay.

The failure of European double medallist Simmonds to qualify in March was one of the most notable shocks.

Florida-based Gemma Spofforth had already made it meaning just one spot was available.

The 20-year-old led from start to finish to win in 59.86, 1.67secs ahead of Ekaterina Avramova.

The women's 100m butterfly saw Lowe edge out Halsall, who had gone out quickly, on the final touch in 57.43 to join Melbourne-based Ellen Gandy on the team.

It was a first personal best for Lowe who joined Swansea ITC following last year's Commonwealth Games after a spell in Florida.

She said: ‘‘I am so surprised I managed to win.

‘‘I usually lose out in close races. It has been a good day for my family.

‘‘My sister went to the X-Factor auditions in Manchester and got four yesses from the judges.

‘‘I am just really happy with the time, I haven't done a PB for three years so it's such a good feeling.''

The fiercely competitive Halsall, who had ankle surgery in December, will now concentrate on the sprint freestyle events in China.

She said: ‘‘That was a good swim for me. I haven't swum that quickly in a long time.

‘‘To be 57.4 now after the year I've had I'll take it any day. I love the freestyle and it was just coming here seeing if I could get the butterfly as well.

‘‘Now I am back in freestyle mode for the worlds. I am a bit disappointed but these things happen don't they?''

World record holder Liam Tancock eased to victory in the 50m backstroke in 25.05.

Hot prospect Siobhan-Marie O'Connor won the 200m individual medley in 2:14.14, inside the qualifying time.

Robbie Renwick (3:48.60) and David Carry (3:49.42) both qualified in the 400m freestyle while Kris Gilchrist claimed a spot in the 100m breaststroke (1:00.99).