The 31-year-old, who runs for Rugby & Northampton, scorched home in 4mins 11.29secs in an indoor international in Vienna.

Her amazing effort was seven seconds faster than she had previously run indoors and five seconds quicker than her best-ever outdoor time.

"I've no idea where that came from," said a delighted Brown, who had to settle for third in the 800m at Saturday's Norwich Union International in Glasgow.

"I was disappointed with my race on Saturday and annoyed that the commentators called me old. They said I was doing all right for my age. Well, I've proved them wrong!

"I've always run better abroad than at home, probably because I don't have to work the day before I race. And this team is brilliant; the management are really looking after us.

"So I was kind of hoping for the World Indoors qualifying time of 4:15. I thought that would be incredible. But once we got going I just got into the zone – and it was incredible. All I have to do now is win the trial!"

Among her rivals at the World Trials and UK Championships at Sheffield on February 9 and 10 will be the Commonwealth 1500m champion Lisa Dobriskey, who Brown has replaced at the top of the winter's UK rankings.

Brown, who competes in another international in Bratislava today, is now seventh in the current world rankings behind six Russian athletes.

Former R&N triple jumper Gary White is also heading to Slovakia.

Meanwhile, Ellena Ruddock and Gemma Werrett were in fine form for Rugby & Northampton AC in the Inter City Indoor Challenge semi-final in Manchester on Sunday.

Six teams competed in the event, representing Birmingham, Sheffield, Glasgow and Edinburgh with R&N athletes representing two of the teams.

Ruddock and Werrett were in the Birmingham side, with Ruddock winning the 200m in 24.50secs, while Werrett won the 60m hurdles in a new personal best of 8.53secs.

Ruddock doubled up in the 60m, where in a blanket finish she recorded 6.68secs to finish fourth, just one hundreth of a second behind second-place.

And to complete a busy day for Ruddock, she ran a blinding last leg in the medlay relay at 200m to bring Birmingham home in second.

In the triple jump, R&N's Linzi Robinson, representing Sheffield, was third while team-mate Claire O'Reilly was fourth.

Birmingham finished second overall to ensure the team a place in the final in Sheffield on February 17.

The second semi-final takes place on Sunday at the Lee Valley Indoor facility in London.

Standings
1 Sheffield 157pts, 2 Birmingham 144, 3 Manchester 132, 4 Edinburgh 130, 5 Newcastle 100, 6 Glasgow 76