US President Donald Trump will do away with 800 years of legal precedent if he expands the use of Guantanamo Bay, a prominent civil rights lawyer has warned.

Clive Stafford Smith, founder of British charity Reprieve, has worked restlessly at the detention centre since its opening in 2002 and has secured the release of several high-profile inmates, such as Shaker Aamer and Moazzam Begg.

After a draft executive order was leaked revealing that Trump plans to expand the use of the facility – including detaining Islamic State (Isis) terrorists for the first time – and to halt all of President Barack Obama's planned transfers and releases of prisoners currently held there, Stafford Smith said that such a move would be catastrophic for US foreign policy.

Speaking exclusively to IBTimes UK, Stafford Smith said: "By saying they are not going to let anyone go, he's basically said habeas corpus means nothing and therefore he's done something that hasn't been done for hundreds of years.

"That is to create an executive order which sentences people to prison indefinitely. That's illegal."

"We know what we should be doing," he added. "We've been doing it for the last 800 years since Magna Carta. You give people fair trials if they've done something wrong."

Trump's executive order, expected to be signed this week, would rescind Obama's 2009 order.

The former president pledged much of his legacy on his campaign promise to close the site and spent his last days in office frantically transferring detainees to countries such as Saudi Arabia and Oman.

By Obama's last day in office, 41 inmates remained at Guantanamo – down from the roughly 800 that were there during its height following the September 11 attacks.

Stafford Smith argues Trump's plan to expand to expand the site's prison population is in line with his aim of stoking anti-Muslim fear and not for any security related reasons.

"Guantanamo is not just illegal and immoral, it's monumentally stupid because it makes the world a much more dangerous place," he said.

"But I would never say that Donald Trump is an idiot – I don't think he's an idiot at all.

"I think he's very calculating and he recognises that the politics of hatred are very effective for a populist politician and when you look at the immigration ban, the majority of Americans support that.

"It's a dreadful idea and it demeans America, but the same is true of Guantanamo.

"Making people hate Muslims is good for business – especially if you're a hate monger and that's what he is. He does this very, very consciously."

Some foreign policy experts believe Trump's plan to expand Guantanamo signals a positive policy change, because it shows a willingness to capture terrorists rather than continue Obama's extra-judicial drone assassination program.

Earlier in February, the new US administration faced a shocking embarrassment after eight-year-old Nawar al-Awlaki was killed in a US Navy Seal raid in Yemen. Her father and older brother, both US citizens linked to Al-Qaeda, were earlier killed in drone strikes under the Obama administration.

Stafford Smith said Trump's expansion of Guantanamo means nothing for the ongoing drone program.

"The solution to two monumentally immoral and misguided policies is not to choose between the two," he said. "It's to not do either of them.

"I'm one of the many people who've said that assassinating people without a trial is worse than holding them without a trial, but Trump's not doing that.

"He's not replacing the assassination program with Guantanamo. He's supplementing the assassination program with Guantanamo and you can bet your bottom dollar he's going to try and assassinate more people than Obama did."