A cloud of suspicion gathered over the head of one of Britain's much-celebrated cyclists on what should have been a bright day for the sport in the UK.

Rob Hayles - Olympic silver medalist and 2005 world champion - was withdrawn from competition just hours before racing began at the track World Championships at his home velodrome in Manchester after he was found to have a haematocrit reading above the permitted levels.

The test - conducted in Hayles' case by the International Cycling Union - measures the capacity of the blood to carry oxygen and was introduced by the UCI in 1997 in a bid to limit the use of the banned drug EPO.

A high haematocrit level is not proof of EPO use and the 35-year-old Hayles issued a statement on his website, saying he was "disappointed and frustrated" at having to miss the two weeks of competition mandatory to anyone with more red blood cells than is deemed healthy.

Blood which is too rich in the oxygen-carrying cells carries the risk of a stroke or heart attack as it is thicker and consequently harder to pump around the body.

Hayles said: "I heard this morning that one of my many blood tests for health screening taken routinely has shown an anomaly - one value was 0.3% above usual expectations.

"I am disappointed and frustrated to have to wait for further tests over the next two weeks before I can compete again. I accept the process is in place for good reason and I agree with it.

"I also accept that I must follow protocol. These anomalies have happened to others across the world, and after two weeks they have been resolved. So I just have to wait for two weeks."

Hayles was due to ride in the individual pursuit - at track centre across the road from Manchester City's Eastlands stadium this evening.

But his place in the British team is understood to have been under pressure for some time.

He was backed by British Cycling's performance director, Dave Brailsford, who said: "I have known Rob a long time and there has never been any doubt in my mind that he has been anything but a fantastic athlete for Britain.

"He does not take drugs."

Both men are putting their trust in further tests to exonerate Hayles, who has won three World Championship gold medals as well as a silver and two bronzes at two Olympic Games.

"Considering the thousands of tests performed on our large squad by now, it not unusual to get one or two such anomalies," said Brailsford.

"Indeed we have had riders in the past who have recorded such anomalies during screening and which have been proved to be entirely normal."

However, Brailsford, who has established Great Britain as the world's dominant force in track cycling and is making inroads in other disciplines, admitted to being dismayed by the news.

Four months out from the Beijing Olympics, he would rather have been helping his riders match the six gold medals they won at last year's worlds.

"You work so hard and put so much effort into being open and transparent but unfortunately these things can happen," he said.

"It's a massive distraction but this is where it's my job to manage."

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