Double Olympic champion Rebecca Adlington fired a warning to her rivals with her quickest 800m freestyle time since last year's world championships.
The 22-year-old's time of eight minutes and 18.54 seconds secured her gold and a second London 2012 qualification berth to follow her 400m win on Sunday.
"I'm so pleased with that swim," Adlington told BBC Sport at the British Swimming Championships in London.
"I've been stuck on similar times for two years so to go quicker is great and hopefully I can do it in the summer."
Adlington added: "I tried to get the crowd involved. The noise was incredible - even before the race it gives you such a buzz. Hopefully I can use it in the summer."
The Mansfield-based swimmer will be joined in the event at the Olympics by 19-year-old Eleanor Faulkner who trains in Sheffield, after she finished second in a personal best time of 8:27.11.
"Becky [Adlington] is my role model and I'm just trying to keep up with her," said Faulkner.
"I'm really shocked that I'm going in an individual event, I wanted to go out and do my best and if I made the relay team great, but I was thinking about 2016, so this is great."
However, there will be no place for world open water champion Keri-Anne Payne in the GB pool team after she finished third.
Elsewhere it was a story of redemption for European champion Lizzie Simmonds and Commonwealth silver medallist Michael Rock.
The pair missed out on Olympic places in the 100m backstroke and 200m butterfly events respectively - but put that right on the penultimate day of the trials.
Simmonds touched in 2:08.67, clear of Stephanie Proud whose 2:09.94 was not enough to qualify for London.
"I was a little bit of a disappointment earlier in the week and it was a case of turning it around," Simmonds told BBC Sport.
"The plan was to make the team in both events, but maybe it's a good thing. The focus has been on 200m with a bit on the 100m, so now I can focus just on the one and hopefully that'll serve me well."
Rock, meanwhile, was delighted with his performance in his less-favoured event.
"It's been a disappointing couple of days, and I've only had a few hours sleep each night, but I had to get things right today. I have and it's such a relief!"
Loughborough's Jack Marriott, who only started full-time swim training last year after a dazzling performance in the 2011 British Championships, was second, but admitted his university studies could prevent him from returning for the second trials in June.
As with the men's 100m freestyle, in the shorter 50m event there were again no athletes able to record times quick enough for guaranteed Olympic selection - Adam Brown won in 22.48.
In the women's 50m freestyle semi-final, European champion Fran Halsall recorded 24.63 to comfortably qualify ahead of Amy Smith.
There was to be no repeat of Eleanor Simmonds' world record-breaking feat from the previous day in the multi-classification swimming races, but 11-time Paralympic medallist Sasha Kindred and 100m breaststroke pair Claire Cashmore and Harriet Lee recorded qualification times for the London Games.
They will confirm their places in the Paralympics GB squad by competing in the British International Disability Swimming Championships in Sheffield next month.
There are only two events on final day of the British Swimming Championships, the women's 50m freestyle and the much anticipated men's 1500m freestyle.
Beijing Olympic silver medallist David Davies, who almost quit the sport last year after being diagnosed with chronic fatigue, qualified quickest with Daniel Fogg second.