A spokesman said the decision to order the detectives out of Aden on Tuesday had been a "minor bureaucratic glitch" and not the official policy of the Yemeni authorities.

However there is still doubt over whether the investigators will be able to interview Islamic militants held after the incident.

The detectives had been carrying out inquiries in Aden and had wanted to interview at least three prisoners arrested over the kidnapping and a further seven held in connection with alleged bomb plots against British targets.

The investigators had asked the governor of Aden for permission to visit the scene of last week's fatal shoot-out, in the southern province of Abyan, but were told they did not have the necessary authority from the Ministry of the Interior and had to return to the capital Sanaa.

Three British tourists and one Australian were killed in a shoot-out between Yemeni security forces and the kidnappers last week.

Sensitive

Diplomats suspect Yemeni pride might have been injured by having foreign policemen investigating on their turf.

The BBC's Frank Gardner: "Yemeni pride may have been injured"

In the past, Yemen has been very sensitive to any criticism, or implied criticism, of its actions by officials or the media in the UK, the former colonial power.

A UK Foreign Office spokesman told the BBC the detectives would be staying in Yemen until they had completed their work.

BBC Gulf Correspondent Frank Gardner said an American police investigation being conducted simultaneously by agents from the FBI did not appear to have encountered the same obstacles.

Diplomats in Yemen said this could be because the Americans were concentrating on the kidnappers' possible links with extremists outside the country rather than investigating the violent way in which the Yemeni Government ended the kidnapping.

Yemen says the kidnappers and the bomb suspects belong to a small, militant Islamic group called Jihad.

A number of militant groups in the Middle East threatened a violent response to the US and UK air attacks on Iraq last month.

Photographic evidence

The BBC has obtained copies of photographs of one of the kidnappers killed on the day of botched hostage rescue attempt. Our correspondent says the picture clearly shows the dead man's wrists bound with thin rope.