Britain's Interior Minister has indicated London would not object to Washington seeking the death penalty against two British Islamic State militants if they are extradited to the United States.

Key points: Britain is not intending to request that the two men be sent to the UK, according to the letter

Britain is not intending to request that the two men be sent to the UK, according to the letter Theresa May's spokeswoman said Britain wanted the militants to be tried in the most appropriate jurisdiction

Theresa May's spokeswoman said Britain wanted the militants to be tried in the most appropriate jurisdiction Sajid Javid is accused of "secretly and unilaterally" abandoning Britain's opposition to the death penalty

Security minister Ben Wallace said Britain was prepared to waive its longstanding objection to executions in the case of captured fighters Alexanda Kotey and El Shafee Elsheikh.

The men are suspected of being two of four militants, dubbed "The Beatles" because of their English accents, who took part in the kidnap, torture and murder of Western hostages.

"In this instance, and after carefully considered advice, the Government took the rare decision not to require assurances in this case," Mr Wallace told the lower house of Parliament.

His statement followed a leaked letter published in the Daily Telegraph from British Home Secretary Sajid Javid.

'Strong reasons for not requiring a death penalty assurance'

The men were captured in Syria in January by a US-backed Syrian force, and Britain and the United States have been in discussions about how and where they should face justice.

According to the Telegraph, Mr Javid wrote to US Attorney-General Jeff Sessions saying Britain was not intending to request the two men be sent to the United Kingdom, saying a successful prosecution in the United States was more likely.

Furthermore, he said Britain would not insist on guarantees the men would not be executed.

"I am of the view that there are strong reasons for not requiring a death penalty assurance in this specific case, so no such assurances will be sought," the letter said.

"As you are aware, it is the long held position of the UK to seek death penalty assurances, and our decision in this case does not reflect a change in our policy on assistance in US death penalty cases generally, nor the UK Government's stance on the global abolition of the death penalty."

A Home Office spokesman said the Government would not comment on leaked documents and Prime Minister Theresa May's spokeswoman said Britain wanted the militants to be tried in the most appropriate jurisdiction.

"It's a long-standing position of the Government to oppose the death penalty … as a matter of principle," the spokeswoman told reporters.

"We are continuing to engage with the US Government on this issue and our priority is to make sure that these men face criminal prosecution."

Alexanda Kotey, left, and El Shafee Elsheikh were captured in Syria in January by a US-backed Syrian force. ( AP: Hussein Malla )

Britain reportedly dropping Guantanamo opposition

The opposition Labour Party accused Mr Javid of "secretly and unilaterally" abandoning Britain's opposition to the death penalty.

"By doing so he is not just playing with the lives of these particular terrorists but those of other Britons — including potentially innocent ones — all over the world," said Labour's Shami Chakrabarti.

The Telegraph also reported that other documents suggested Britain would not oppose the men being sent to the US-run Guantanamo Bay military facility.

However, the Home Office spokesman appeared to reject this saying: "The UK Government's position on Guantanamo Bay is that the detention facility should close."

American journalist James Foley was beheaded by an IS cell that reportedly included Elsheikh and Kotey. ( Supplied: Nicole Tung )

The most notorious of the four so-called "Beatles" was Mohammed Emwazi, known as "Jihadi John", who is believed to have been killed in a US-British missile strike in 2015.

He became the public face of Islamic State and appeared in videos showing the murders of US journalists Steven Sotloff and James Foley, US aid worker Abdul-Rahman Kassig, British aid workers David Haines and Alan Henning, Japanese journalist Kenji Goto and other hostages.

The mother of James Foley said she did not want the men to be executed if found guilty.

"I think that would just make them martyrs in their twisted ideology," Diane Foley told BBC radio.

"I would like them held accountable by being sent to prison for the rest of their lives."

Reuters