Terror suspects from the UK could soon be jailed in Jordan - a country long accused of torturing its prisoners - under a deal struck last week between the two governments.
Jordan has stepped up its 'war on terror' on home-grown militants
Officials in London and Amman say the agreement safeguards the human rights of all deportees.
But rights groups have voiced alarm, arguing that the deal does not deter torturers and will not let governments off the hook if torture does occur.
International law forbids extradition to countries where there is a risk of mistreatment, "no matter how good your assurance" that torture will not take place, says Christoph Wilcke of Human Rights Watch.
"We have had such diplomatic assurances in the past and they have not worked," he told the BBC News website.
'Fear of persecution'
Another rights group, Amnesty International, has said "the assurances of known torturers... are not worth the paper they are written on".
Amnesty says it has received several complaints of mistreatment at the hands of Jordan's security services - the majority from people accused of terrorism.
It recently reported claims by two Yemeni men who said they were suspended upside down and beaten on the soles of the feet in detention in Jordan. One man said he was threatened with electro-shock torture and sexual abuse.
Among those who could be affected by last week's deportation deal is Abu Qatada, a radical cleric who was granted asylum in the UK more than a decade ago.
Abu Qatada is wanted in Jordan for alleged terror attacks
According to Jordanian officials, he could soon be returned to his home country - in all likelihood to face retrial for a life sentence he received in absentia for plotting a series of blasts.
Although the British Home Office will not comment on the specific grounds that secured Abu Qatada his right to remain in the UK in the early 1990s, a spokesman said London grants asylum to anyone with "a well-founded fear of persecution".
According to Joe Stork of Human Rights Watch, "all the good reasons that prevented the UK from deporting people to Jordan... remain unchanged" by the latest agreement.
"There is still torture in Jordan, especially with regard to security suspects," he said.
'Different legal systems'
Human Rights Watch says it objects to diplomatic assurances against torture because they are "generally subject to the limits of diplomacy and lack effective means to secure compliance".
A Foreign Office spokesman told the BBC News website no penalty had yet been decided for a party that strayed from the agreement by torturing a deportee.
Amnesty interviewed Yemeni men who testified about torture
However, he said, were torture to occur, it would be a matter of "considerable concern".
A spokesman for the British Home Office said the agreement did not guarantee any deportees will continue to be treated as they have been in the UK.
"All we're trying to say to the Jordanians is you can't harm them, you can't torture them. We still can't hold their hand on everything that then happens over there," he said.
"We can't say - you've got to adopt our law. It is a completely different legal system. It might be that they can over there detain without charge for longer than we can."
Jordan's interior minister, meanwhile, has said the agreement will "guarantee the civil rights of individuals under existing Jordanian laws and the international human rights conventions".
Rights groups remain sceptical about the agreement.
"By seeking Jordanian promises to treat these returned persons differently, the UK is confirming that the risk of torture continues," says Mr Stork of Human Rights Watch.
The group says apparent safeguards against torture, included in the deal, will have no real effect.
The agreement stipulates monitors will be allowed to visit deportees in detention at least once a fortnight - a "ludicrous" provision, according to Mr Wilcke of Human Rights Watch, who believes the visits must be more frequent.
"Torture is not always visible," he said.
Terrified prisoners often do not report mistreatment because they have "to face the torturer the very next minute", as soon as the rights monitor walks out, Mr Wilke added.