Allegations of British collusion in torture have widened to Egypt, where a young British man says he suffered appalling mistreatment during a week of illegal detention while being interrogated on the basis of information that he says can only have come from the UK.

The development comes after the Conservative leader, David Cameron, said there needed to be a full inquiry, not just to discover whether crimes had been committed by British officials but to establish whether the government’s “moral authority” has been maintained.

Azhar Khan, a 26-year-old who has seen a number of friends jailed for terrorist offences, says Egyptian intelligence officers who detained him when he flew into the country last July forced him to stand on the same spot for five days, with little rest, while beating him and subjecting him to electric shocks. Throughout this time, he says, he was asked detailed questions about his friends and associates in the UK.

The Foreign Office has confirmed that Khan was detained in Egypt for a week last July and, after being pressed repeatedly, admitted that it knew that Khan had subsequently complained that he had been tortured. The Guardian understands that Khan’s allegations of mistreatment are supported by medical evidence.

Khan says he was handcuffed and his feet shackled throughout the five days he was tortured, and that he was naked but for a hood kept over his head. He also says he could hear other detainees being tortured in the same large room, including one man with a British accent.

The Guardian has learned from a reliable source that MI5 had an interest in another person who was in detention in Egypt at the same time as Khan, and that the security service knew that there was every possibility that this individual would be tortured.

The allegations will fuel calls for an independent inquiry into the conduct of Britain’s security and intelligence officers in the so-called war on terror.

Gordon Brown is resisting an inquiry, saying that the attorney general will decide whether the police should be asked to investigate.

In addition to Cameron’s calls for an inquiry, however, Lord Carlile of Berriew, the government’s independent assessor of counter-terrorism legislation, said this month that a judicial inquiry was needed to examine Britain’s role in the US policy of rendering suspects to foreign prisons where they can be tortured.

Andrew Dismore, the MP who chairs parliament’s Joint Committee on Human Rights, says an independent inquiry may need to be held to examine MI5’s role in the torture of British terrorism suspects after the foreign secretary, David Miliband, and the home secretary, Jacqui Smith, refused to appear before his committee to answer questions.

Professor Manfred Nowak, the United Nation’s special rapporteur on torture says he has “been in regular contact with the British government” to raise his concerns about the role of British intelligence officers in the interrogation of terrorism suspects who have previously been tortured.

Last week a highly critical UN report condemned Britain for breaching basic human rights and “trying to conceal illegal acts” during counter-terrorism operations.

A policy governing the interrogation of terrorism suspects in Pakistan that led to British citizens and residents being tortured was devised by MI5 lawyers and figures in government, according to evidence heard in court during a hearing brought on behalf of Binyam Mohamed, the British resident freed from Guantánamo last month.

Since Mohamed’s detention in Pakistan in 2002 a number of British terrorism suspects have been tortured there, both before and after interrogation by MI5 officers; and they and their lawyers say there is clear evidence that British officials have been aiding and abetting their mistreatment.

However, Khan, from Slough, Berkshire, is the first British national to allege British collusion in torture in Egypt.

Khan is the former brother-in-law of a convicted terrorist, Omar Khyam, and was an associate of other members of a group led by Khyam who are serving life sentences in the UK after being convicted of plotting to blow up targets including the Ministry of Sound nightclub in London and the Bluewater shopping centre in Kent. He was arrested at the same time as Khyam in March 2004, but released a few days later without charge.

He and a friend flew to Cairo on 9 July last year having told friends that they planned to have a short holiday in Egypt. Khan was detained immediately on his arrival, but no attempt was made to detain his travelling companion, who says he left the airport and alerted the British embassy.

Khan says he was held in a room at the airport for about 24 hours before agreeing to sign a document in Arabic, having been told by uniformed police that it would lead to the return of his passport.

He says he was then hooded and handcuffed and bundled into the back of a vehicle between two men, one of whom apologised to him in English and said: “This is our job, this is what we have to do.”

In an account of his subsequent mistreatment given to his solicitor as well as to relatives and close friends, Khan says he was driven for a short distance and taken into a building where the hood was removed. He could see that he was in some sort of prison with barred windows. He was stripped naked, handcuffed and his feet shackled and the hood placed over his head once more.

Khan says he was led along a corridor into a room where a number of people were being tortured from time to time. He says he was beaten around the body with sticks and subjected to occasional, unexpected electric shocks. His captors shouted at him and beat him if he tried to sit or lie down, he says, although he was occasionally allowed to rest. He says he received little food or drink.

Around him, he says, were a number of other people who were also being beaten and tortured, including one man who spoke English with a British accent and prayed during beatings. From other cells within the prison he could hear screaming from both men and women throughout the day and night.

During interrogations, which took place twice a day, he says he was asked in English about his friends and associates in Slough, Berkshire, in Crawley, West Sussex, and in east London.

He was asked about the bomb plot and about the bomb itself. However, the questions concerned not only the men convicted of conspiring to cause explosions but others whose names had never entered the public domain. His torturers, Khan says, even knew the name of the sister who married Khyam.

Khan says he was also asked about discrepancies between a statement that he had given to British police at the time of his 2004 arrest and later comments that he made while visiting friends in jail.

During other sessions he was asked about his childhood, faith and mosques he had attended, in a series of questions similar to those put to his friends four years earlier.

He says that after five days of torture he was taken out of the room, his shackles removed and his clothes returned.

He says he was then put into the back of a vehicle, driven across the city and thrown out of the car with a hood still over his head. When it was removed he found himself in a public place with a uniformed police officer standing next to him. He was taken to a police station and a statement was taken from him.

He says he met a number of British consular officials and told them that he had been tortured. The following day he flew to Heathrow, where he was detained for questioning under counter-terrorism legislation. He told the officers what had happened to him and was released without charge.

Khan remains deeply traumatised by his experience and has been receiving a range of medical and professional care, including treatment for internal bleeding that persists eight months after his release.

The torture of detainees in Egypt has been well-documented over many years by human rights groups and the US state department.

According to Amnesty International, about 18,000 people detained without trial are languishing in Egyptian prisons in “degrading and inhumane” conditions.

The organisation says that methods of torture routinely employed by the country’s principal intelligence agencies, the Mukhabarat al-Aama and Mubahath el-Dawla, include blindfolding, beating, suspension in painful positions, electric shocks, drugging, rape and death threats.

The UK Foreign Office reported in January last year: “One of the key human rights concerns in Egypt is the widespread mistreatment of detainees and use of torture in police stations, especially in cases involving political detainees. The government has taken some steps to address the problem, such as allowing semi-independent prison inspections, improving prison conditions, and paying compensation to victims of torture.

“There have also been a few court cases against police and prison officers accused of mistreating detainees.

“But the basic problem still remains, and we actively encourage the Egyptians to tackle it.”