Letter to president about Binyam Mohamed was blanked out, say campaigners as they prepare for Guantánamo prisoner's release to UK

US defence officials are preventing Barack Obama from seeing evidence that a former British resident held in Guantánamo Bay has been tortured, the prisoner's lawyer said last night, as campaigners and the Foreign Office prepared for the man's release in as little as a week.

Clive Stafford Smith, the director of the legal charity Reprieve, which represents Ethiopian-born Binyam Mohamed, sent Obama evidence of what he called "truly mediaeval" abuse but substantial parts were blanked out so the president could not read it.

In the letter to the president [PDF] , Stafford Smith urges him to order the disclosure of the evidence.

Stafford Smith tells Obama he should be aware of the "bizarre reality" of the situation. "You, as commander in chief, are being denied access to material that would help prove that crimes have been committed by US personnel. This decision is being made by the very people who you command."

It is understood US defence officials might have censored the evidence to protect the president from criminal liability or political embarrassment.

The letter and its blanked-out attachment were disclosed as two high court judges yesterday agreed to reopen the court case in which Mohamed's lawyers, the Guardian and other media are seeking disclosure of evidence of alleged torture against him. Mohamed's lawyers are challenging the judges' gagging order, claiming that David Miliband, the foreign secretary, changed his evidence.

In a judgment last week, Lord Justice Thomas and Mr Justice Lloyd Jones stated repeatedly that Miliband claimed the US had threatened to stop sharing intelligence with the UK if information relating to Mohamed's alleged torture was disclosed. Miliband subsequently denied the US had applied such pressure. The case will be reopened next month.

After a meeting with Mohamed's US-appointed military lawyer, Lieutenant Colonel Yvonne Bradley, Miliband said yesterday that the US had granted permission for Foreign Office officials to visit Mohamed. The Foreign Office said the officials would be joined by a Metropolitan police doctor, who would accompany Mohamed back to the UK if he is released.

Stafford Smith said he believed this trip was to check Mohamed was fit to fly after the hunger strike that he has maintained for over a month. He stressed that no date for his client's release had been fixed, but "I think we're talking about a week, I sincerely hope so".

Millband said the US administration had agreed to treat Mohamed's case as "a priority", adding that Britain was working with Washington for "a swift resolution". Bradley said later: "We haven't been given any specific date about Mr Mohamed's release."

Earlier, she told a press conference that Mohamed's treatment "would make waterboarding seem like child's play".

Bradley and Stafford Smith yesterday met in private with members of the intelligence and security committee, the group of MPs and peers facing mounting criticism in Westminster over claims it failed to effectively scrutinise the activities of MI5. Stafford Smith said he told the committee it would have been "absolutely impossible" for it to have cleared MI5 of involvement in the torture of Mohamed had it seen 42 key documents in the case – as he has – that Miliband says cannot be released for reasons of national security.

Bill Delahunt, a senior Democrat congressman and chairman of the House of Representatives subcommittee on human rights and oversight, said: "We cannot let our governments stonewall ... I take offence at the idea that secrecy is being maintained in order to preserve national security." He told the all-party committee on rendition: "The treatment of detainees has done great harm to the security of both our nations."

Lieutenant Colonel Nigel Wylde, who worked in intelligence in Northern Ireland, told the committee: "The use of torture is utterly counterproductive because it breeds hatred against us and encourages people to become extremists."

David Davis, a former shadow home secretary, said torture was wrong morally and legally, ineffective and undermined the safety of British people. "Was the government involved, was it a matter of policy or a matter of freelancing – failure of policy or a failure of control?"

The Liberal Democrat foreign affairs spokesman, Edward Davey, said: "Miliband's bad judgment in blocking the courts from publishing this evidence of torture is being compounded by his refusal to press the new Obama administration to disclose this evidence freely."