The 24-year-old clocked a winning time of 21.92 seconds, breaking Mark Foster's time over the splash and dash distance of 21.96 secs, set back in 2008 in the era of the now banned controversial super suits.
"It’s my first time back under 22 seconds in a long time, so I’m delighted with that," said US-based Brown, who was well inside the qualifying standard for next month's World Championships in Barcelona.
"Mark [Foster] has been a great model for me growing up, so I'm really chuffed to finally beat his best time.
"It’s been five years since he set it, so I’ve been gunning for it all of this time. And it has been four or five years since I last set a personal best myself, so I am really happy.
"Training has been going really well and actually I have been focusing on the 100m freestyle, so that was a bonus."
Fran Halsall claimed another national title after winning the 50m freestyle with a dominant performance at Ponds Forge.
Halsall has long been Britain's undisputed number one sprint freestyler and proved it again with a winning time of 24.54 secs that was nearly half a second faster than nearest rival Amy Smith.
It's four years since the 23-year old won 100m freestyle silver at the World Championships in Rome and she is now eyeing a return to the podium in Spain.
"It was pretty tough because we had the semi and the final in the same session," said Halsall.
"We won’t get that schedule at worlds, so it makes it very difficult to swim a really good time.
"But I’m happy with that, I’ve been consistent – under 25 seconds – for most of the year so looking forward to Barcelona that’s a really good sign."
And Robbie Renwick is confident he has done more than enough to secure World Championship selection after victory in the 400m freestyle.
Two-time Olympian Renwick took gold with a commanding performance, clocking 3:47.02, more than a second and a half inside the qualification standard.
He finished well ahead of nearest rival Daniel Fogg to defend his title and underline his favourites status.
But making the plane to Spain is still no formality, with team officials restricting the squad size to just 35 in a bid to add more competitiveness into the national team after disappointing London Olympics.
"I was inside the qualifying time so I should be at the World Championships now," said Renwick.
"It is a bit of a relief to get the first swim out of the way and it kind of takes the pressure of a little bit, knowing that I have qualified and with the 200m and 100m left it was great to get the 400m out of the way."