Correspondent Frank Gardner: Investigators are trying to find out if the shoot-out was necessary

Brian Smith, David Holmes and Sue Mattocks told a news conference at London's Gatwick Airport they were amazed to be alive following the "barrage of fire" between their kidnappers and Yemeni soldiers on Tuesday.

Four travellers - Britons Margaret Whitehouse, Dr Peter Rowe and Ruth Williamson and Australian Andrew Thirsk - were killed as the kidnap drama drew to a close.

The party of British, American and Australian tourists - who were on an "adventure holiday" organised by UK firm Explore Worldwide - were abducted on Monday in the southern Yemeni province of Abyan.

Bloody denouement

Hostage David Holmes: "Laurence said to the bandit 'You have killed my wife'."

Dr Rowe's wife, Dr Claire Marston, was injured and remains in hospital in Aden.

A plane containing the victims' coffins arrived in London at around 2300 GMT on Friday.

Holmes: Offered a ceremonial dagger

The Yemeni Government has been accused in some quarters of bungling the rescue attempt but the hostages were unwilling to criticise the Sana'a authorities.

Mr Smith, a 52-year-old postal worker from Peterborough, said: "None of us has any idea who fired the first shot. We simply do not know."

'Not a tidy operation'

Ms Mattocks, a 43-year-old school teacher from Ramsgate, Kent, said: "Any operation like that is never going to be tidy."

Sue Mattocks says of the victims: "I am desperately, desperately sorry."

She said she was concerned about an "anti-Yemeni feeling" which she had noticed in some of the press coverage of the hostage incident.

"Yemen is a sovereign country and they made their decision," said Ms Mattocks.

Mattocks: Looking forward to returning to work

Asked how she felt about the four victims and their families she said: "Desperately, desperately sorry, particularly as we have spent the last 48 hours with the man who has been bereaved. It's been awful".

Mr Holmes, a 64-year-old retired teacher from Grimsby, paid tribute to Mrs Whitehouse's husband, Laurence, and described how he had grappled with one of the "bandits" after his wife was shot dead.

Laurence Whitehouse, his voice breaking with emotion, talks about his ordeal

He said the man shot dead Mrs Whitehouse and then began to retreat, using Mr Whitehouse as a "human shield".

Mr Holmes said: "He dragged him past me at which point Laurence, realising what had happened, said: 'You have killed my wife, you have killed my wife' with great intensity.

Whitehouse: Saw his wife killed

"He grabbed the arm of the bandit and at that point the revolver went off and Laurence has two holes through his shirt but he was not hurt."

Mr Smith said the abductors mentioned the bombing of Iraq only once and added: "They were aware of Iraq but they did not hold us responsible for our government's actions."

'Dignity and courage'

Mr Smith said he was amazed to be alive and said everyone in the group had shown tremendous "composure, dignity and courage" in the circumstances.

Explore Worldwide spokesman Derek Moore gives his condolences to the bereaved and speaks of his hopes for the future

Asked how Mr Whitehouse was coping, he said: "With great courage and dignity beyond any manner of comprehension, unbelievable courage."

Mr Holmes said Mr Thirsk had shown absolutely no fear when facing the barrel of a gun and added: "When he was shot twice again he showed great courage."

He said: "There was not anybody in the group who flinched in the face of this ordeal. We were all incredibly calm. I don't know why."