Claire Marston, a Briton, and American Margaret Thompson flew out of Aden on Sunday morning.

A Foreign Office spokesman said Mrs Marston would be moved to hospital on arrival in the UK.

Her husband, university lecturer Dr Peter Rowe, 60, from Durham, was one of four people who died when the Yemeni authorities tried to rescue 16 Western tourists by kidnapped Islamic militants.

Teacher Margaret Whitehouse, 52, from Hampshire, Ruth Williamson, 34, an NHS employee from Edinburgh and Australian Andrew Thirsk, 35, also died.

The last of the former hostages touched down at London's Gatwick airport just before 20.00 GMT on Sunday on a Yemen Airways flight. Other passengers on the plane said both women had been on stretchers thoughout the journey.

Eight of the Britons who survived the shoot-out arrived back in Britain on Friday night, but Mrs Marston was too badly injured to return home and remained in hospital. However she is now said to be in a stable condition.

'Unanswered questions'

There is still uncertainty over what exactly happened in Yemen. Liberal Democrat Foreign Affairs spokesman Menzies Campbell has called for a House of Commons statement on the hostages.

He said: "There are far too many unanswered questions, such as the tactics employed by the Yemeni forces, the identity of the kidnappers and whether there was any prior warning.

The foreign secretary should make a statement to the Commons as soon at it resumes in a week's time, Mr Campbell said.

The Home Office was unable to confirm reports that pathologists have begun investigations to establish whether the hostages were killed by their captors or the Yemeni security forces.

Four Scotland Yard detectives are in Yemen alongside an American FBI team investigating the circumstances of the killings.

It has emerged that Yemen security chiefs knew days before the kidnapping that Islamic militants were planning to attack a British target.

The Yemenis uncovered the plot after arresting two extremists but they failed to alert British diplomats, who learnt about the threat only after the four hostages had been killed.

If British diplomats had been alerted, the Foreign Office could have advised the tour company Explore Worldwide and other tourists about the increased risk.