Hicks, originally from Adelaide, has been held at Guantanamo Bay in Cuba since 2002 after being captured by US forces the year before in Afghanistan allegedly fighting alongside the Taliban.
He faces a military commission trial in October on charges of conspiring to commit war crimes, attempted murder and aiding the enemy.
During a chat about the Ashes cricket series with his Pentagon lawyer Michael Mori, Hicks revealed his mother was British and had never taken out Australian citizenship.
A law change in 2002 entitled him to register as a British national.
His lawyers believe if he claims British citizenship it may help him escape his detention, and Major Mori has since lodged an application on his client’s behalf for dual Australian-British citizenship.
The British government refused to allow any of its nine Guantanamo Bay inmates to be tried by military commission because it said the trials fail to uphold basic standards of international justice.
It successfully demanded its citizens be repatriated, and all were set free.
“He told me he’d never felt very partisan about the Ashes and wouldn’t much mind if England took the series — because his mum had never claimed Aussie nationality and still carried a UK passport,” Major Mori told Britain’s Observer newspaper.
“My jaw hit the floor. I asked him, ‘Do you realise that may mean you’re legally a Brit?’ We both knew that the implications of that could be stunning.”
One of Hick’s American lawyers, Michael Ratner, has told ABC radio he believes his client has a good chance of becoming British.
“It would certainly be a bad application of the law to somehow discriminate against David Hicks by saying he, because he is in Guantanamo, can’t have the citizenship of his mother – that would be very unusual,” said Mr Ratner.
“I expect … that David Hicks will be a British citizen. At that point of course we … know the British have fought really hard to get their citizens out of Guantanamo and have condemned the very kind of military commissions that David Hicks is now going to face some time in October.”
David McLeod, one of Hicks’ Australian lawyers, said Canberra is aware of the move, but there are no details on whether any plans are afoot to influence the British government’s decision.