With a Union Flag draped across his shoulders, Alistair Brownlee slowed to walking pace as he crossed the finishing line in Hyde Park. Yet if the elder brother's victory elicited deafening roars of delight from crowds in London and his native Leeds the arrival half a minute later of Jonathan Brownlee to snatch bronze, despite a 15-second penalty for a minor infringement of the rules, was greeted with equal if not greater fervour.

"To get two of us – two brothers – two British brothers on the podium you couldn't ask for any more," said Alistair, 24, as Jonathan, two years his junior, was led away in a wheelchair to the resuscitation area after collapsing at the race's climax.

The Brownlees, the hugely popular sons of two doctors from Bramhope in Leeds, look set to become Britain's most famous sporting siblings since Bobby and Jack Charlton and further boost the popularity of one of the world's fastest growing pursuits.

Hundreds of thousands of fans had taken to the streets of London to cheer them on while hundreds more gathered around big screens and crammed into the brothers' local pub in Yorkshire to watch the drama unfold. Yet those with most at stake were the Brownlees' parents who, riven with nerves and the anxiety that accompanies a sport where competitors routinely drive themselves to the point of exhaustion, had arrived at the Olympic venue four-and-a-half hours before the race began.

Once satisfied their youngest son was all right, the relieved couple described witnessing their sons' success as "unreal" – despite their 40-hour-a-week training schedule and lifelong determination to achieve this moment. "You don't think that those boys running through that line and winning those medals are your sons," said Cath Brownlee. Her husband, Keith, a consultant specialist in the treatment of cystic fibrosis, said he felt "pride, elation, relief … it's just wonderful".

Alistair however had been entirely without nerves before the start. "I was like a kid at Christmas, I just wanted to get out and race," he said.

But he was scathing of the decision to give his little brother a time penalty, which he incurred for mounting his bike fractionally too early during the transition between the swim and the cycle. "I've never been a fan of penalties at the best of times. I think it's ruining the sport. It's not about giving people penalties. It's not about official decisions whether they should get 15 seconds or not," said Alistair.

In Leeds, 500 people had impatiently counted down the younger Brownlee's 15 seconds in the sin bin. As he burst back into podium contention the crowd gave a huge roar of excitement. Among them were half a dozen nurses from Leeds General Infirmary, where Dr Brownlee works, and members of the High Performance Triathlon Unit at Leeds Metropolitan University, where the brothers train.

Athlete Robert Bridges, 22, said the pair were always marked out by their determination and extraordinary regime which sees them in the pool from 7am every day. "They are really nice guys – just typical lads. I'm so glad for Alistair. I know he really wanted this gold and would have been gutted if he had been beaten," he said.

More than 200 people packed into the Old Sun Hotel in Haworth, West Yorkshire. Dave Woodhead, a family friend, said: "Alistair is muck and nails. He's a Yorkshire animal. Gold is what he wants and his motto is 'Who dares, wins', so for me the outcome was a done deal."

The Brownlees' success brings the number of gold medals won by Yorkshire athletes to five – placing the county level with ninth-placed Germany and accounting for a quarter of the national team's haul.