A spokesman for the Department of International Relations and Cooperation, Nelson Kgwepe, said the man had not been identified.

''The South African High Commission in London is in touch with the authorities in the UK investigating the case. The body of the stowaway is still in London and will remain there while the investigation is under way,'' said Kgwepe.

The police in Britain are treating the death as ''non-suspicious'' and have confirmed that the man was not a member of the aircraft's crew or a passenger on the Boeing 747 .

But Deidre Davids, communications manager in Cape Town for Airports Company South Africa, said a security guard saw a man scaling a fence on Wednesday. The guard pursued the man, who ran in the direction of the runway.

An aircraft was ready to take off on the runway and the guard lost sight of the man.

"Given that it was at night and the uncertainty relating to where the man had disappeared to, a full sweep of the runway, as well as of the airfield, was ordered.

''If anything had happened to the man while running on the airfield, it is important to make sure that the runway, in particular, was clear of foreign objects. Failure to do so could result in an incident with incoming and outgoing aircraft," said Davids.

The man was not found.

But Davids said when alerted about the stowaway found on board the British Airways plane at Heathrow: "We knew it was the same man."

Security has been beefed up at the airport.

A security guard now watches over all international flight departures and arrivals after dusk, and security at the perimeter fence has been strengthened.

Stephen Forbes, a spokesman for British Airways, said: "Our thoughts are with the individual's family.

"We are liaising with the South African authorities and the Cape Town airport as they investigate."