Don celebrates his World Triathlon victory in September 2006

In October 2006 he was banned for three months for missing three out-of-competition tests in 18 months.

That expired on 25 December but under a BOA bye-law the world champion remained ineligible for Olympic selection.

But a BOA Appeals Panel said there were "significant mitigating circumstances" and overturned that Olympic ban.

Don said he was "delighted" with the news.

"I am relieved and happy to be reinstated and I can now concentrate 100% on gaining Team GB selection and performing well in Beijing," he said.

"If something good can be taken from my case, then it has been to highlight the importance of the need to keep your UK Sport whereabouts information up to date."

UK Sport chief executive John Steele said it accepted the BOA's ruling and appreciated the importance the Association attached to its out-of-competition testing programme, but warned other athletes of their responsibility to be available for testing.

"Athletes across all sports should take particular notice of the Panel's warning that this decision does not set a precedent and the BOA's statement that any future cases may not be dealt with so sympathetically," he warned.

The Panel accepted the findings of a British Triathlon Association tribunal that Don had no intent to take any prohibited substance and had never attempted, or had the intention of, avoiding the rules.

It also noted that he had requested help with using the system and had written to the BTA asking for further training in the period between the first and second missed tests, and took into account that there were some problems with the new testing system.

But the panel was keen to point out to other athletes that the finding of innocence of actual doping would not have been enough on its own to support his appeal.

It was particularly critical of Don for missing the final test, when he failed to be at a location he had chosen at the time he had said he would, which they described as "indisputably careless and irresponsible".

Don's case could have implications for Commonwealth 400m champion Christine Ohuruogu, who was banned for 12 months in September 2006 for missing three out-of-competition tests and is also banned from the Olympics because of the BOA's rule.