Iraqi authorities received a body today that they believe is one of the British hostages taken in Baghdad in 2007, Foreign Secretary David Miliband said tonight.
A Downing Street spokesman said: "The Prime Minister was deeply saddened that a further body, which the Iraqi authorities believe to be one of the British hostages taken in 2007, has been passed to the British Embassy in Baghdad.
"A process is now under way to urgently establish identity. The Prime Minister is in close touch with the Iraqi prime minister about this case.
"He will leave no stone unturned in the Government's efforts to secure the release of the remaining hostages.
"The Prime Minister's thoughts are with their families at this extremely difficult time."
In a statement, Foreign Secretary David Miliband said it was not yet possible to "definitively confirm" either that the body was a hostage or which one it was.
But he said: "My thoughts and those of all of my colleagues in Government are, of course, with the families of the British men kidnapped in Iraq.
"We are in close touch and informed the families of all five hostages of these developments earlier this afternoon.
"It is particularly distressing for them again to hear bad news, without final confirmation, that one of their loved ones has died.
"We are determined to keep this period of uncertainty for the families to a minimum."
Mr Moore is still believed to be alive, Mr Miliband said.
Mr Miliband said the Government remained in "close contact" with those in Iraq who could be able to help secure the release of the hostages.
"Our cross-government effort by teams in London and Baghdad continues unabated," he said.
"Today's distressing news will not diminish our determination.
"Hostage-taking is never justified. Britain's long-standing policy is well-known: We talk to anyone who might be able to help but we do not make substantive concessions to hostage-takers.
"This is not an easy policy to follow - sometimes it is agonising - but it is right."
He went on: "I renew my call, on behalf of the British Government and the British people, to those holding the hostages to return them to their loved ones."
Mr Miliband said he would make a further announcement "in due course" once formal identification of the body had been made and the families of all the hostages had been informed of the conclusions.
A spokesman for GardaWorld, which employed four of the men, said: "We're continuing to try to do everything that we can, working with all of the authorities involved for the recovery of these individuals."
He would not comment further while the identity of the person remains uncertain.
The five Britons - Mr Moore and his four bodyguards - were seized by about 40 armed men wearing police uniforms at the finance ministry in Baghdad on May 29 2007.
The bodies of Mr Swindlehurst, 38, from Skelmersdale, Lancashire, and Mr Creswell, 39, originally from Glasgow, were handed over to Baghdad officials in June.
The families of security guards Mr McMenemy, from Glasgow, and Mr MacLachlan, from Llanelli, South Wales, were told by the Foreign Office in July that their loved ones were "very likely" to have died.
Responsibility for the kidnapping was at first pinned on Muqtada al-Sadr's Mahdi Army.
It was thought to be a retaliatory attack for the killing by British forces of the militia's commander in Basra, southern Iraq, a week earlier.
But al-Sadr's followers denied responsibility and suspicion fell on splinter groups which the US believes are controlled by Iran.
The kidnappers, calling themselves the Islamic Shiite Resistance in Iraq, have issued several videos featuring the captives and making demands.
In February last year a video broadcast by Dubai-based TV station Al-Arabiya showed a bearded and tired-looking Mr Moore asking Mr Brown to free nine Iraqis in exchange for the British hostages.
He said: "All I want is to leave this place. I tell Gordon Brown the matter is simple: release their prisoners so we can go."
Mr Moore also appeared in another video which was sent directly to the British Embassy in Baghdad in March.
The release of leading Shiite insurgent Laith al-Khazali by US forces on June 6 had sparked fresh hopes that the Britons could be freed.
Al-Khazali is a senior member of Asaib Ahl al-Haq, or the League of the Righteous, which has been linked to the kidnapping.
An inquest in June heard that Mr Swindlehurst and Mr Creswell suffered gunshot wounds, although it is not clear exactly when they died.Reuse content