Jackson, who was to have defended an unbeaten run of 35 races stretching back to last August, picked up a bug after returning from Tuesday's meeting in Madrid where he ran the fastest 110m hurdles of the season - 12.99sec. Malcolm Arnold, Britain's chief coach who also coaches Jackson, said: 'Colin is in bed and does not feel able to compete. It's a setback for us.'
Jackson was also an important member of the sprint relay squad in Britain's bid to match their World Cup performance of two years ago when they finished second behind Africa.
They have a world class replacement in Tony Jarrett, but the Londoner has been unable to maintain the high standards he set for himself this summer and he was disappointed with only a bronze medal at last month's European Championships in Helsinki.
Even before Jackson's withdrawal, the British men had their work cut out to compete with an African team which looks eminently capable of retaining its title against opposition from the home country, the Americas, Asia, Europe, Oceania, Germany, and a weak United States team.
The women, who will do well to get into the top three, are competing under the threat of a retrospective disqualification if Diane Modahl loses her appeal against an impending four-year ban after a drugs test.
Yesterday there was an apparent entente cordiale between the British authorities, who insisted on keeping their women's team in the competition pending a conclusion to Modahl's case, and the International Amateur Athletic Federation, which had hinted that Britain had a moral duty to pull out.
Primo Nebiolo, the IAAF president, stressed that his organisation agreed with the British position; Peter Radford, the BAF executive chairman, said relations between the two bodies were 'first class'. But Modahl's husband and coach, Vicente, has accused the IAAF of treating his wife 'like a criminal'.
'The security in Portugal surrounding the samples would appear to be less than adequate,' he said. 'The testing does not take into account medical conditions. When this is over and she is declared innocent, the world of athletics and of international sport generally will have to take a long, hard look at itself and its procedures.
'Diane would have come back from Canada with a gold medal, but she was robbed of that opportunity. The people who did this also took her integrity and treated her like a criminal - fortunately they could not take her dignity.
'But now her eyes are empty, she just wants to go to sleep and wake up when it is all over.'
Since her return home from the Commonwealth Games in Victoria, the Modahls have become recluses at their home in Sale, Cheshire, and have taken legal advice on her case.
Vicente Modahl claims there are three ways the tests could have shown positive - her samples, or food, were spiked at the athletics meeting in Lisbon where she gave the two urine samples; she had a rare medical condition; or there was an accident at the laboratory.
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