Great Britain team members are facing a tough choice in the build-up to this summer's Olympic Games in Beijing. Should they wear the Speedo LZR Racer and risk losing valuable contracts with other suit-makers, or wear the brands that they are financially tied to and lose a 2 per cent advantage on the clock that could mean the difference between winning medals and not reaching finals?

The claims made for the LZR Racer by Speedo have been shrugged off as marketing hype in some circles, but 18 world records since February 16 - all within a fingernail of being 2 per cent better than the previous best time of the athlete in question - and similar gains on the clock from hundreds of athletes in several countries have provided ample proof that the new technology is enhancing performances.

On the eve of the world short-course championships, which begin today in Manchester, Mark Schubert, the United States head coach, told The Times: “My advice to athletes is, ‘You have a black-and-white decision - the money or the gold medal.' And it's going to be a real test of character.

“There is no doubt the suit makes a difference and there is no doubt that there is one manufacturer that's put millions into research while the other manufacturers are more into fashion. Nobody at this level [world-class athletes] can afford to give up 2 per cent. It is not rocket science.”

To some extent, it is rocket science: technology developed by Nasa, the space agency, which worked with Speedo, is used to bond the panels on the world's first seamless suit. The big breakthrough has been in compression and the positioning of support panels around the girdle that provide a level of core stability for swimmers not present before. Ryan Lochte, the US swimmer who is in line to be the star of the show in Manchester with several gold-medal chances, echoed many others when he spoke of legs that never tire and a new ability to hold optimum body position throughout races. “It feels like I'm floating, like I'm swimming downhill,” he said.

Publicly, adidas and Arena, the main rivals of the Nottingham-based Speedo, have let it be known that they will not penalise athletes who wear other apparel when racing for a national team sponsored by Speedo. But The Times has spoken to three athletes who claimed to have been threatened with loss of contract and financial support if they wear the Speedo suit. One said: “I'm really worried. I've got to do what's best for me in the pool, it's obvious, but it means I lose the support.”

Before a meeting on Saturday in Manchester between suit-makers and Fina, the international governing body, Schubert said: “The other manufacturers need to put the effort in, catch up and quit whining. Some are contracted to an inferior product and those manufacturers need to let go.”

Michael Scott, the Britain performance director, said: “We are a professional team, with cutting-edge sports science at our disposal. The suit is technical equipment.”

The overall Britain Olympic team will wear adidas in Beijing, but swimmers are allowed to wear any swimsuit, unbranded unless adidas. The problem is, the LZR is distinct without branding.

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