Ekyepong, 21, a member of Nigeria's 4 x 400 metres relay squad, was discovered carrying stimulants, and was sent back on the same plane.
Games officials, preparing for the arrival of the Queen and Prince Philip, played down the incident, saying it showed that their efforts to fight drug abuse were working.
'There are measures to catch the people that are not playing by the rules. People who are cheating are going to get caught,' one official said.
Team coordinator Dan Enajekdo said Nigerian authorities had taken pains to stress to their athletes that drugs were unacceptable. 'We don't want to win by hook or by crook. Our sportsmen and women are supposed to be ambassadors,' he said. 'This is a bad egg and he has been sent back.'
There was also controversy yesterday when a recommendation in the official newspaper Spirit for a treatment for wasp and bee stings had to be withdrawn because the kit contains adrenalin, a banned substance.
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