OLYMPIC bronze medallist Jo Jackson launched her bid to qualify for next month's World Championships in Shanghai with an impressive heat swim to progress quickest to tonight's 200metres freestyle final at the British Gas ASA National Championships in Sheffield.

Jackson, from Richmond, North Yorkshire, claimed two silvers and one bronze medal at the World Championships two years ago in Rome, but ill health and asthma blighted Jackson for 18 months from the autumn of 2009.

The Loughborough swimmer failed to secure a place on the Great Britain team for Shanghai next month at the first trials in Manchester in March in either an individual event or on a relay.

Following Manchester, she switched coach from Kev Renshaw to Ben Titley, a move which coincided with a general improvement in her health and by extension training and competition.

Speaking last week Jackson was noticeably more positive and this morning at Ponds Forge saw the 24-year-old qualify in one minute 59.67 seconds.

Rebecca Turner (2mins 00.08) and former double Commonwealth champion Caitlin McClatchey (2:00.16) were second and third fastest.

Also through is double Olympic champion Rebecca Adlington although she will not be swimming tonight's final as she has already qualified for China and European 400m individual medley champion Hannah Miley.

World record holder Liam Tancock was fastest into the 50m backstroke final.

The Loughborough swimmer touched in 25.07 as he warms up in his bid to retain the world crown he claimed in Rome.

The failure of Lizzie Simmonds to qualify in March was one of the most notable shocks in Manchester.

The friendly rivalry between GB team-mates Simmonds and Gemma Spofforth has spurred the pair on with the two of them sharing two gold and two silver medals at last year's European Championships.

Florida-based Spofforth has already made it on to the team and is not in Sheffield this week but Simmonds produced a smooth, controlled swim in the 100m backstroke heats.

The Loughborough student touched in 1:00.63 ahead of Georgia Davies who will be looking to rival Simmonds for the remaining spot over two lengths.

Fran Halsall and Hartlepool's Jemma Lowe look set for a real tussle for the one place available in the 100m butterfly.

Ellen Gandy has already qualified so the pair will battle it out tonight with both impressing in the morning heats.

Lewis Smith (400m freestyle), Iain McMillan (200m butterfly), Kris Gilchrist (100m breaststroke), Lucy Spencer (200m individual medley and Anastasia Christoforou (50m breaststroke) all qualified fastest in their respective events.