Dr Keith Brownlee tells a story that sums up the attitude that has made his son, Alistair, the world’s leading triathlete and a hot favourite to win Olympic gold in London next year.

The 23-year-old has already been a world champion at junior, under-23 and senior level and in September clinched his second world title.

Dr Brownlee recalls how at the start of one season, when triathlon was a passionate hobby rather than a way of life, Alistair decided he would improve his running by getting up at 6.30am every day to do a circuit of the local woods around Horsforth, dragging his dad along.

Brownlee senior was less than enthusiastic about the new schedule and would seek out his son’s alarm clock and turn it off. But Alistair was determined and hid the clock, ensuring a valuable training opportunity was not missed.

The rise of the baby-faced swimmer, cyclist and runner – who is a member of Bingley Harriers Athletics club and a former pupil at Bradford Grammar School – has been phenomenal.

But even more remarkable is that his closest challenger this season has been his 21-year-old brother Jonny.

The pair finished first and second in this year’s Dextro Energy ITU World Championship Series.

Over the past three years in World Championship Series races in which at least one of them has competed, there has only been a single occasion where a Brownlee has not been on the podium.

Despite this, Dr Brownlee, who works in the paediatric cystic fibrosis unit at Leeds General Infirmary, admits his primary focus remains simply making sure both sons complete the race in good health.

His worries are understandable. Last year Alistair suffered heat exhaustion during the Hyde Park race and collapsed over the finish line. Mum Cathy, who is also a doctor, jumped over the barriers to be with her son as he was rushed to the medical tent.

“We joke that Alistair came tenth and Cathy came 11th,” Dr Brownlee says.

Hot weather makes him nervous and he began checking the long-range forecast two weeks before this year’s race.

“There are a number of feelings,” Dr Brownlee said. “Immense pride at what each of them are achieving, and there is pride that they’re doing it together.

“But the most overwhelming feeling is relief when they finish intact and without injury. I know how far they’re pushing themselves.

“I’ve ended up in resuscitation tents at least twice with each of them. But I think they’re getting older now and more mature and better suited to Olympic distance. I’m a little bit less anxious than I used to be.”

The most remarkable thing for an outsider is the degree to which each brother thinks about the other, before, during and after each race.

They may be competing against each other for the sport’s biggest prizes but it is very much a team effort.

They live together, along with a couple of friends, in Alistair’s house in the village of Bramhope just outside Horsforth and have been taken to the hearts of the pensioners that make up the rest of their street, who are happy to take delivery of bike wheels and invite their young neighbours around for tea.

Dr Brownlee has no doubt having each other has been a major factor in their success.

He says of their relationship: “Most of the time they’ve been the best of friends. Occasionally they would fight over Monopoly, chess, football, all the usual things.

“They’ve always been incredibly competitive with each other. Even now they time each other on who is the fastest to empty the dishwasher or hang out washing.

“I always hoped they would support each other. At the end of the day they’re bright and they realise they’re really fortunate to be doing something they really enjoy doing, and they’re able to do it because they’re quite good at it, and they’re quite good at it partly because they’ve got each other.”

Getting carried away is clearly not a trait that runs in the Brownlee family. Even when Alistair won the world junior title in 2006 his parents did not expect him to become a full-time athlete.

That decision was a big one, for it meant dropping out of Cambridge University, where he had completed one term of a medical degree.

“Clearly there were massive concerns,” says Dr Brownlee. “But we always felt the most important thing was that he was doing something he enjoyed.”

Even now, Dr Brownlee had no idea of the buzz his sons have generated.

It is no surprise, then, that his concerns about the Olympics centre around qualification and fitness rather than the impact medals and celebrity status could bring.

“I suspect they’ll choose to go back to their house in Bramhope and go cycling with their friends,” he adds.