When Martyn Rooney, one of the handful of British fledgelings with true lip-smacking potential, was first called up to represent his country on the global stage, it ended in embarrassment. Flushed with excitement, he arrived at the team camp for the World Junior Championships in Grosseto, Italy, in 2004 and was told there was a problem. “Both my parents are Irish and I didn't have a British passport,” the Croydon-born quarter-miler said. “That was it. I was out. Gutted. Devastated.”

The World Juniors are taking place in Bydgoszcz, Poland, this week, but Rooney has moved on. He has his passport, is rising through the rankings and has even felt emboldened enough to give Jeremy Wariner, the superstar at 400metres, the benefit of his thoughts. “I saw him [at the Golden Spike meeting] in Ostrava, in the Czech Republic,” he said. “Usually, Wariner does not say a word to anyone except his training partner. There is an aura about him. He is amazing. We had a few words, though. I said it was good for the sport that LaShawn Merritt had beaten him. He agreed.”

Rooney knows that he is not in Wariner's class, but he is one of a string of athletes approaching the Aviva National Championships and Olympic trials in Birmingham this weekend with burgeoning confidence. His best this season is the 45.19sec he ran in Geneva on May 31 and while Wariner heads the world lists this year with 43.98, Rooney is confident of dipping below 45 seconds soon.

That would put him into the big league and the select club of 12 Britons who have done the same. Yet Rooney, 21, believes that his future lies in the 800metres, which is where Britain truly craves a star to revive the public's passion for the sport. “I was an 800metres runner for a long, long time and I love it,” he said. “I like the tactics, the fact you're running against people rather than in lanes, the fact you can use your elbows. It's a serious part of the plan, but for the moment I look at what Iwan Thomas did in the 400metres and that's an inspiration.”

Thomas, at 34 the old warhorse and best Briton of the lot, is ploughing on, treading a fine line between nostalgia and not knowing when to quit. Rooney, meanwhile, showed how he has the mentality for what he terms real racing by running 44.17 in the last leg of the relay at the European Cup in Annecy, France, last month.

What Rooney now wants is a race against the big guns. He has noted how Merritt, someone he knows well from the junior ranks, has twice beaten Wariner this season. Peer pressure, he believes, is the secret of taking himself to the limit. “I will be disappointed if I don't make the final in Beijing,” he said matter-of-factly. That may not sound much to the layman, but to make the top eight in the world under the most intense pressure would be a personal victory.

“Having watched Merritt as a junior, I'd have said he was the one to watch and it's made the event more interesting,” Rooney said. “Wariner agreed with me when we spoke. He said it would push him to run quicker. Who will win? If you put Wariner under pressure in the last 20 metres and he is not 100 per cent, then you have a chance. Next year the balance of power may change, but this year I'd go for Wariner. Definitely.”

Based in Loughborough, where he is coached by Nick Dakin, Rooney cuts a relaxed figure, but says that that is his way of preparing. “Wariner comes from this group that is incredibly focused, but if I focus that much I am sick,” he said. “I try to stay relaxed.” So he listens to an eclectic mix of music ranging from Slipknot to Frank Sinatra. He used to enjoy rugby, where he played wing and outside centre, until his height - he is 6ft 5in - condemned him to the second row, and he found athletics. He has already come a long way since being forced to sit out the World Juniors in Grosseto. “I still get stick about it but I learnt a hell of a lot from that trip,” he said. This time he has the passport. The stamp of approval may be coming, too.