A British Islamic State fighter who is believed to have carried out a suicide bombing in Iraq was a former Guantanamo Bay detainee, according to reports.

The bomber, named by the group as Abu Zakariya al-Britani, is said to have detonated an explosives-filled vehicle in a village to the south of Mosul.

The 50-year-old, also known as Jamal al Harith or Jamal Udeen, was suspected of terrorism by the Americans but freed from the US detention centre in 2004 after lobbying by the British government.

He reportedly alleged torture and received £1 million in compensation from the UK government after his release.

According to the BBC, the bomber was a Muslim convert born Ronald Fiddler.

Zakariya al-Britani turned to Islam in the 1990s and travelled to the Pakistani city of Quetta in 2001 for what he claimed was a religious holiday.

He has insisted he tried to enter Iran when the US invaded neighbouring Afghanistan, but was captured and imprisoned by the Taliban on suspicion of being a UK spy.

Around 850 individuals of national security concern have travelled to join the conflict, according to figures published by the Government last year.

Of those, just under half have returned to the UK and approximately 15% are dead. 

The terrorist's brother, Leon Jameson, 53, identified him as the man equipped with explosives in the IS propaganda video.

Mr Jameson told The Times his brother had "wasted his life" and added: "It is him, I can tell by his smile."

Former prime minister Tony Blair came under fire for the reported lobbying by his government for the Guantanamo Bay prisoner's release.

The Daily Mail quoted Tory MP Tim Loughton as saying: "So much for Tony Blair's assurances that this extremist did not pose a security threat.

"He clearly was a risk to Britain and our security all along.

"It adds insult to injury that he was given £1 million in compensation because of Blair's flawed judgment that he was an innocent."