Four businessmen who were arrested in the United Arab Emirates have been tortured into making confessions and could face the death penalty, according to a United Nations report and a legal opinion obtained by their British lawyer.

The plight of the four men, who variously hold Libyan, American and Canadian citizenship, has been taken up by Labour’s justice spokesman, Andy Slaughter, who is concerned about UK links to the Gulf state and previous complaints by Britons about being tortured in Dubai.

The legal opinion by Geoffrey Robertson QC, a former UN judge, says the four businessmen – Salim Alaradi, who has Libyan and Canadian nationalities, Kamal and Mohamed Eldarrat, who have Libyan and US nationalities, and Issa al-Manna, a Libyan – have been wrongly accused of funding a terrorist organisation. They are due to go on trial in the secretive state security chamber court in Abu Dhabi on Monday.

Alaradi was holidaying with his family at a beach hotel in Dubai when he was arrested last summer by the State Security Agency (SSA), according to Robertson’s report. He was not permitted to notify his family or any lawyer of his arrest.

“[Alaradi] was in secret detention – at an air force base, it is believed – [where] he claims he was tortured, a claim corroborated by serious bruising observed on his body, by similar claims by several of the men who were detained at the same time and have now been released, and by evidence of torture and ill-treatment in the UAE gathered by Amnesty International and Human Rights Watch,” the report states.

Alaradi said he was subjected to sleep deprivation, chained in a stress position, hung upside down and beaten on the soles of his feet. “He was made to carry heavy weights while being beaten, subjected to waterboarding techniques and blasted for lengthy periods by ice-cold air,” Robertson said. “His brother was in an adjacent cell, and heard him screaming.”

The organisations that they are alleged to have funded, the February 17 Brigade and Libya Dawn, are paramilitary forces that have been allied to the west and are not on the Libyan government’s list of banned groups, according to Robertson.

The UN working group on arbitrary detention (UNWGAD) will publish a report on the four men on Monday calling for their immediate release from custody. It says: “All of them were deprived of the right to challenge their arrest and detention before the judicial authorities and subjected to enforced disappearance, secret and incommunicado detention. [We] received reliable information on the acts of torture [inflicted on] the four victims...”

The report documents claims that the men were subjected to electric shocks, whipped, had guns held to their heads, were drugged and “hung with a rope around the neck”. Some said they had been placed in a freezer for up to 45 minutes.

In its response to the UN panel, the UAE said: “[The four men] are completely free to choose, appoint and meet with a lawyer according to the rules of procedures governing correctional institutions.”

The UN working group is the same body that produced a critical report this month declaring that the WikiLeaks founder Julian Assange, who is resisting extradition to Sweden for questioning about an alleged rape, was being held under arbitrary detention in the UK.

Prof Mads Andenæs, a former chair of the working group, told the Guardian: “Some states try to block rulings against the UAE, based on the usual ‘your friend’s friend is your friend, and your friend’s enemy is your enemy’ … The UAE has had much more moderate responses to previous UNWGAD rulings against them than the UK. I hope that this not now going to change after the inappropriate UK responses in the Assange case.”

Labour’s Slaughter said: “The UK has a special relationship with the UAE which should be reviewed in the light of the UN working group report. This case rings a warning bell to the UK government, which is sending international development funds to UAE to support the development of legitimate institutions, and selling them large quantities of arms.”

British human rights groups such as Reprieve have documented similar complaints from UK citizens held in the UAE, who have said they were tortured into making confessions.

Sue Willman, a partner at the law firm Deighton Pierce Glynn and a member of the UK Law Society’s human rights committee, said: “British citizens have also reported torture in Abu Dhabi and Dubai, where other Brits enjoy relaxing holidays. In the past year, I have been contacted by a growing number of ex-detainees and their families all complaining of torture and arbitrary detention there.

“As my client faces the death penalty in a kangaroo court, it is time for the UK government to make it clear to its partners in the Gulf that it can no longer tolerate such flagrant breaches of basic human rights”.