Briton Feroz Abbasi is also being held

Mr Mubanga was understood to have had fled to Zambia after fighting in Afghanistan alongside al-Qaeda and the Taleban, according to The Sunday Times.

It is thought Mr Mubanga was held by the Zambian authorities for some time before being handed over to US authorities.

The Foreign Office spokesman said consular access and information were requested while Mr Mubanga was being detained in Zambia, but that request was refused.

The spokesman said: "As a dual national, Mubanga was treated as a Zambian national when detained there.

"Under international law we are unable to interfere in the judicial processes of other countries."

Courier

The son of a former Zambian government official whose family moved to Britain in the 1970s, Mr Mubanga reportedly lived in Wembley, north west London, before moving to nearby Dollis Hill, The Times Sunday said.

He is reported to have worked as a cycle courier in London before travelling to Afghanistan, where he is said to have attended several al-Qaeda training camps.

The Foreign Office had no record of a seventh, un-named Briton being held in the base, as reported in the newspaper.

The other Britons being held in Guantanamo Bay are Shafiq Rasul, 22, Asif Iqbal, 21, and Ruhal Ahmed, 20, all from Tipton in the West Midlands; Feroz Abbasi, 22, from Croydon, south London; and Jamal Udeen, 35, from Manchester.

They were all captured in Afghanistan.