Be Number 1 swimmer Jackson, who also claimed a silver medal in the 400m freestyle discipline on Sunday, was the second-fastest qualifier for tomorrow’s final, behind fellow Briton Rebecca Adlington

Olympic champion Adlington set the quickest time of 8:20.53 in this morning's heats while Jackson, for her part, was only marginally slower in winning her heat in 8:20.80.

And the pair's hopes of a one-two in the 16-length final were given a further fillip by the withdrawal of the 200m and 400m gold medallist Federica Pellegrini.

Both Britons dominated their heats from the start, Adlington beating Beijing silver medallist Alessia Filippi by more than three seconds while Jackson's victory margin of 15 metres was even more dominant.

The top four from Beijing - Adlington, Filippi, Lotte Friis and Camelia Potec - and Jackson make the top five qualifiers.

Jackson said: "I felt really tired this morning going into that, so to come away with that time I'm really happy. I'll just rest and hopefully have a good race. I didn't get back until 11pm last night because I had to have a drug test and it was pretty much straight to bed. Both Becky and I were feeling it this morning, but that is what we've been training for.”

Both Jackson and Adlington were both part of the GB quartet that demolished the British and European record by more than three and a half seconds in last night’s 4 x 200m relay final. But they, together with Caitlin McClatchey and 18-year-old Jazmin Carlin, still had to settle for bronze behind China and USA, both in times that obliterated the previous world record that was established by Australia at the 2008 Olympics in Beijing. It was, nevertheless, a British performance that provides firm foundations from which to construct a relay team capable of winning a gold medal at the 2012 London Olympics.