Tancock was seven tenths quicker than nearest rival Ryan Bennett as he clocked 25.53 seconds in his 50m backstroke heat at Ponds Forge.
The 24-year old is looking to book his place in England's squad for October's Commonwealth Games this week - with the 100m backstroke and freestyle his other aims.
"I am training the best I ever have done, I am lifting heavier weights than I ever have done in the gym and I am fully prepared," said Tancock.
"Now I have to swim the fastest I can and learn from each swim I have and use it as a spring board to the next one.
"The British Championships are different this year because the English, Scottish and Welsh teams all have different qualifying dates and times they need to hit throughout the year so not everyone will be at 100 per cent."
Tancock broke the 50m backstroke world record during the 100m race at last year's British Championships - and the lowered the mark again when he clocked 24.04 on way to world gold in Rome last summer.
However, with new regulations on swim suits now in force, he admits more record breaking is unlikely during the next six days.
"I broke my first world record in Sheffield and it is one of the fastest racing pools around but records aren't a focus this week," he added.
"I swam quickly the other week in the new Speedo wear but no-one really knows how it is going to affect things."
Story courtesy of morethanthegames.co.uk (From David Jordan, Sportsbeat, in Sheffield)