The men, who were working as civilian contractors, were kidnapped by armed militants at the Iraqi Ministry of Finance in Baghdad on May 29 2007.

Britain's ambassador to Iraq, Christopher Prentice, urged the hostage-takers to free the captives and called on anyone with information to contact the UK authorities.

Relatives also spoke of their agonising year-long wait and of their belief that the men would eventually be released.

From the British embassy in Baghdad, Mr Prentice recorded a video message in English and Arabic aimed primarily at Iraqis.

One of the hostages has been named as IT consultant Peter Moore, from Lincoln, who was working for BearingPoint, an American management consultancy.

The others, who were employed by Canadian security firm GardaWorld to guard Mr Moore, have not been officially identified, but it is believed two are Welsh and two Scottish.

A man identified only as Colin, father of a hostage called Alec, said the families "had to believe" the outcome would be positive.

The kidnappers, calling themselves the Islamic Shiite Resistance in Iraq, have released two videos of the captives over the past year.

On December 4, a film was broadcast on Dubai-based TV station al-Arabiya warning that one hostage would be killed unless British troops were withdrawn from Iraq. One of the men, named as Jason, was shown in the clip complaining that the kidnapped men felt they had been "forgotten".