Lawyers acting for a Libyan politician who accuses MI6 and the CIA of secretly sending him and his pregnant wife to be tortured by Muammar Gaddafi will on Monday fight a UK government attempt to prevent those responsible from being brought to justice.

Abdel Hakim Belhaj and his wife Fatima accuse the government, MI6 and the former foreign secretary Jack Straw of false imprisonment, conspiracy to cause injury, abuse of public office and negligence.

Belhaj's abduction in 2004 with the help of MI6 came to light when documents were found in Tripoli after Gaddafi's fall two years ago. They revealed that MI6's Sir Mark Allen congratulated the Libyan intelligence chief Moussa Koussa on the safe arrival of the "air cargo", and noted that "the intelligence [on Belhaj] was British".

The government is expected to argue that the case should be thrown out because it would damage UK-US relations. It is also expected to argue the case is beyond British courts' jurisdiction given the alleged unlawful acts took place with other states' help, notably the US and Libya.

Government lawyers have indicated that if necessary they will seek to have the case heard in secret courts set up this year by the Justice and Security Act.

Whitehall's use of secret courts to save itself from embarrassment, rather than to protect national security as claimed, has been dramatically exposed by the revelation that the Ministry of Defence tried to prevent the disclosure of the treatment of prisoners captured by UK forces in Afghanistan.

Part of a secret high court judgment which has now been disclosed reveal that an alleged Taliban leader, identified only as Detainee 806, was handed over by the British to a prison in Kabul despite a moratorium banning the transfer of prisoners there because of its reputation for torture.

The judgment, now declassified, states that Dr Amrullah Saleh, the chief of the Afghan National Directorate of Security, persuaded British officials to hand over Detainee 806, after giving his personal assurance that he would be treated humanely and would be allowed weekly visits from the British.

According to a witness statement by a senior Foreign Office official – which was also kept secret at the original court hearings in 2010 – the decision to comply with Saleh's request was taken by then Labour foreign secretary David Miliband and armed forces Minister Bill Rammell on the grounds that the prisoner could more easily be prosecuted in Kabul.

Evidence in the newly declassified judgment, obtained after a legal challenge by the Mail on Sunday, showed that despite Saleh's promises, Detainee 806 "disappeared" for a month. When he finally met two British army personnel, he told them he had been beaten with steel rods about his legs and feet, punched in the head, torso, arms and testicles, and deprived of sleep for days. On a subsequent visit, he said he had also been whipped with electric cables. Some of his injuries were photographed.

The judgment said the judges could not determine the prisoner's credibility, but it added: "We consider that the only safe way to proceed is on the assumption that the allegations are true."

Nevertheless, the judges said in 2010 that there was no good reason to make his claims public. "The public interest considerations in favour of non-disclosure ought in our view to prevail."

The MoD had asked for the evidence and judgment in the case to stay secret to protect national security and preserve relations with the Afghan government. They also said disclosure might put prisoners at risk of reprisals.

Referring to the Afghan prisoner case, the former shadow home secretary David Davis told the Mail on Sunday: "Far from protecting national security, this was about hiding political embarrassment.

"The fact David Miliband broke our own moratorium and handed over a prisoner to be tortured is a clear matter of public concern, which using a secret court covered up. This is a very bad harbinger for the secret justice procedures which the new Act creates."

Neither Miliband nor Rammell responded to the paper's requests for comment.

Sapna Malik, a partner at the law firm Leigh Day representing Belhaj and his wife, said on Sunday: "[This case is] the latest attempt by the UK government to deploy dubious legal arguments and political scaremongering to defer having to answer the simple allegations at the heart of this case, to stand up in court and admit what the UK's role was in this sordid affair and who authorised it.

"All our clients want to hear is the truth followed by an apology. This would cost much less than the expensive delaying tactics the government is using to fight this case."

Malik added that the British government had paid out more than £2m to the family of the Libyan dissident Sami al-Saadi, who was also rendered back to Gaddafi, but Belhaj and his wife wanted to pursue the case so the full evidence could be heard.

Cori Crider of the law charity and human rights group Reprieve said: "Instead of coming clean and apologising, which is all Mr Belhaj and his wife are looking for, the government is fighting tooth and nail to stop the case coming to trial."

Belhaj was living in China in 2004, after heading a low-level insurgency against the Gaddafi regime during the 1990s as leader of the Libyan Islamic Fighting Group.

He and his wife decided to seek asylum in the UK but were detained in Malaysia and Bangkok, where they were handed over to US authorities before being rendered to Tripoli.