Why are we asking this now?

The former shadow home secretary David Davis used the legal protections of parliamentary privilege to accuse British security services of "outsourcing torture". Mr Davis cited Rangzieb Ahmed, from Rochdale, an al-Qa'ida leader who was jailed for life in the UK for directing terror. The Conservative MP claims the security services allowed Ahmed to go to Pakistan so they could alert the authorities who, he claims, arrested and tortured him. Mr Davis said he had "a whole load of corroborative evidence" to support his claim regarding Ahmed.

What exactly was the alleged role of the British security services?

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Mr Davis said that although British police and the security services had enough surveillance material to charge Ahmed, they still allowed him to go to Pakistan. Once there, British intelligence suggested to the Pakistani authorities he should be arrested. A list of questions to be put to Ahmed was drawn up by the security services and Manchester police, said Mr Davis. Ahmed has said he was whipped with tyre rubber, beaten with staves and had three fingernails pulled out.

Is Rangzieb Ahmed the only alleged victim?

No. Government security sources have told newspapers that as many as 15 British suspects may have been rendered and tortured in Pakistan, Afghanistan, Bangladesh and north Africa. The most prominent allegations have been made by a British resident, Binyam Mohamed, who was arrested in Pakistan in 2002. Mr Mohamed, who has never been charged with a terrorism offence, was questioned after being seized at Karachi airport in April 2002 travelling on a false passport. He was sent to an interrogation centre where, he says, he was hung up for a week by a leather strap around his wrists. Among his interrogators were officials from America's CIA. He was later visited by two British intelligence officers, one called John. The torture stopped when they came, Mohamed said. He said John told him: "I'll see what we can do with the Americans." He didn't see John again.

Are there others?

Jamil Rahman, a British civil servant, claims Britain was complicit in assault, unlawful arrest, false imprisonment and breaches of human rights legislation over his alleged ill-treatment while detained in Bangladesh. Mr Rahman, who has never been charged with a terrorism offence, says that he was the victim of repeated beatings over a period of more than two years at the hands of Bangladeshi intelligence officers, and he claims that a pair of MI5 officers were blatantly involved in his ordeal.

Has Britain been involved in rendition?

It depends how one defines rendition. If it is standing by while allowing allies to unlawfully fly British terror suspects around the world the UK may well be guilty. Mr Mohamed was flown to Morocco after being held incommunicado in Pakistan, where he was interrogated by an MI5 officer. From Morocco, he was rendered to Kabul's notorious CIA prison where he says he was held in darkness for weeks on end. MI5 telegrams to the CIA show security service officers fed the US with information on Mr Mohamed when he was allegedly being tortured in Morocco. MI5 has said it did not know where he was or in what conditions because the CIA refused to say.

Is there more evidence?

Yes. There is further evidence that Britain has allowed its territory in Diego Garcia to be used by the Americans to illegally transfer other suspects to detention camps around the world. The British Foreign Secretary David Miliband had to make an embarrassing admission to Parliament after the US informed the Government that they were mistaken when they had previously said that no suspects were flown to the Indian Ocean island.

Why did the British security services allow the Americans to interview UK citizens?

After 9/11 Britain got sucked into the the war on terror led by US security services, which sanctioned the use of torture in certain circumstances. In the immediate aftermath of the event, Tony Blair stated that Britain stood "shoulder to shoulder" with the US administration and between 2002 and 2004 there was an intimate sharing of intelligence information between the CIA and their British counterparts. As their relationship closened, so British citizens ended up under the control of US authorities. In a court case involving Mr Mohamed, the ruling of two judges, Lord Justice Thomas and Mr Justice Lloyd Jones, in 2008 was: "The relationship of the United Kingdom Government to the United States authorities in connection with [Mr Mohamed] was far beyond that of a bystander or witness to the alleged wrongdoing."

Are the police investigating?

They are. Scotland Yard has been asked to look at the allegations made by Mr Mohamed to see whether MI5 officers are guilty of complicity in torture. The Attorney General, Lady Scotland, said in a written statement that she had given the allegations of possible criminal wrongdoing "very serious consideration" and felt there were sufficient grounds to launch a criminal investigation. But she stopped short of conceding a full judicial inquiry, which many critics have demanded.

Have British agents been directly involved?

Yes. Shaker Aamer, a British resident who is still being held in Guantanamo Bay, claims that an MI5 or an MI6 officer was present while he was being tortured and abused by US agents in Afghanistan in 2002. Mr Aamer, 42, is a Saudi citizen who has a British wife and five British children living in south London. A claim letter sent to government lawyers alleges: "UK intelligence services officers were present whilst Mr Aamer was beaten. They provided information and encouragement to his US torturers. They made no attempt to stop his ill-treatment or any enquiries into his well-being."

What is Britain's position on torture?

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MI5 never officially comment. However, the position of the UK Government is that it condemns torture, in line with the United Nations Convention Against Torture, which we signed up for in the 1980s. Officially, the last torture warrant issued in England was in 1641. More recently the Prime Minister has announced a review into MI5 operations.

What will happen next?

The Liberal Democrats and the human rights charity Reprieve, who represent Mr Mohamed, are already demanding a full judicial enquiry into the role of Britain's security and intelligence services. Ed Davey, the Liberal Democrat foreign affairs spokesman said: "These are incredibly serious allegations of complicity in barbaric acts of torture and breaches of international law. There must be complete faith in the way the investigation is carried out if the public's trust, and Britain's standing in the world, is ever to be restored."

How high does the scandal go?

It is impossible to say but it seems unlikely that Britain officers and agents were acting without recourse to authorities high in government. Of particular interest is what the former foreign secretary Jack Straw knew of the involvement of security and intelligence services activity between 2002 and 2004. It seems almost inconceivable that when alarm bells started sounding about the US treatment of detainees in the war on terror, senior British politicians were not kept in the loop.

Does Britain outsource torture?

Yes...

* There are more than one or two isolated cases of Britain's alleged complicity in torture and rendition

* Britain was very close to the US at the start of the war on terror and turned a blind eye to CIA excesses

* MI5 agents admit they sent questions to their CIA counterparts to help them question suspects

No...

* No case has proved that any UK suspect was tortured by a third-party state on the instructions of British agents

* The security and intelligence services don't believe that torture delivers truthful information

* At worst UK agents are guilty of not asking questions of foreign agencies