Two men captured by Iraq and shown on TV are civilian lorry drivers employed to deliver food to Iraqi prisoners of war, the Ministry of Defence has said.
One of the prisoners of war shown on al-Jazeera TV
Defence Secretary Geoff Hoon criticised Qatar-based satellite channel al-Jazeera for showing footage of the captured men and of dead British soldiers.
An MoD spokeswoman told BBC News Online the drivers - who are thought to be Kenyans - were sub-contractors to the British Army working through an unnamed company in Saudi Arabia.
She said they had been part of a convoy with a military escort, but had become separated after it was halted by a "civil disturbance".
Mr Hoon said the decision to broadcast TV footage of two dead British soldiers had been a "flagrant and sickening breach of the Geneva convention".
And he condemned the Iraqi regime for "parading" the prisoners of war on television.
Mr Hoon said anybody guilty of war crimes would be held personally responsible for their actions.
Earlier al-Jazeera reporter Jawad Omari defended the station, saying it was determined to "show our audience the truth, even if it is a dirty war".
In a briefing at the Ministry of Defence, Mr Hoon said coalition forces were making good progress.
He said that significant discoveries had shown categorically that Iraqi troops were prepared for the use of weapons of mass destruction.
The MoD could not confirm the nationality of the two captives shown in the TV footage.
But Al-Jazeera said it believed they were Kenyans working for the British Army as lorry drivers.
The Kenyan High Commission in London was investigating the claims.
The MoD told BBC News Online it appeared the two drivers had been captured after they failed to make a turning when the rest of the aid convoy did.
A spokeswoman said: "It would be quite normal to hire civilian contractors."
She could not say how many civilians were working for the MoD in Iraq, or whether the policy was under review.
The men should be given prisoner of war status while they were held, she added.
Their employers have been informed of their capture.
The MoD says the dead men shown by al-Jazeera are thought to be soldiers who went missing during fighting around al-Zubayr, near the southern city of Basra.
One appeared to have been shot in the chest, but the other's injuries were unclear.
The footage also showed their wrecked vehicle, with armed civilians climbing over it.
Their families have been informed.
Shadow Foreign Secretary Michael Ancram criticised Iraq for allowing the dead men and prisoners to be filmed.
"This is another blatant example of the depths to which this regime is prepared to sink.
"Just as they have no compunction about murdering their own people in their tens of thousands, their depravity knows no bounds in their treatment of prisoners of war."