The UK tolerated "inexcusable" treatment of US detainees after the 9/11 attacks, MPs have found.

The Intelligence and Security Committee (ISC) said it was "beyond doubt" the UK knew how the US handled some detainees.

The ISC found no "smoking gun" indicating a policy of deliberately overlooking such cases.

The chair of the parliamentary group on extraordinary rendition, Ken Clarke, called for an independent inquiry into the UK's role, "to get to the truth".

According to the ISC report, the UK continued to supply intelligence to allies in 232 cases where British officials knew or suspected mistreatment.

Prime Minister Theresa May said British personnel had been working in "a new and challenging operating environment" which some were "not prepared" for.

She added "it took too long to recognise that guidance and training for staff was inadequate", and said British intelligence and the Army were "much better placed to meet that challenge".

The ISC rejected claims by intelligence agencies that the cases detailed were no more than "isolated incidents".

The report added: "That the US, and others, were mistreating detainees is beyond doubt, as is the fact that the agencies and defence intelligence were aware of this at an early point."

BBC security correspondent Gordon Corera said the report showed there was "no evidence of direct mistreatment" by British intelligence agencies, but there were "13 cases where spies witness first-hand a detainee being mistreated by others".

He added that the ISC criticises the UK's foreign intelligence service MI6, and its listening service GCHQ for playing "a role in enabling some detentions".

The report adds "more could have been done" by security agencies and ministers in Tony Blair's government to try and influence US behaviour.

Former Foreign Secretary Jack Straw, who was responsible for overseeing GCHQ and MI6, said he was not aware of the activities or approach of the agencies.

He said the report shows that "where I was involved in decisions I consistently sought to ensure that the United Kingdom did act in accordance with its long-stated policies, and international norms".

He said "many lessons... have since been learnt".

The ISC launched its three-year investigation after plans for the independent judge-led Gibson Inquiry collapsed. It studied documents, interviewed former detainees and three ex-officials.

But, in the report, the ISC says the government "denied" the committee access to "officers who were involved at the time" of the UK's involvement in rendition.

Chairman of the ISC, Dominic Grieve, said: "By 2017, we had reached the point in our inquiry where we had covered the breadth of the issues but wished to examine certain matters in greater detail: in order to do so we needed to hear from the officers who were involved at the time.

"The government has denied us access to those individuals."

British citizen Moazzam Begg, previously held in Guantanamo Bay, criticised the inquiry's scope as inadequate, saying "we still don't know the process of accountability".

Speaking about his own detention, he said: "British intelligence agents were physically there watching as I was hooded, shackled, with a gun to my head, threatened with being sent to Syria or Egypt if I didn't co-operate.

"There was the sound of a woman screaming in the room next door, that I was led to believe was my wife being tortured. British intelligence agents knew all about this."

Although there is no evidence US rendition flights transited through the UK, there is evidence that two detainees went through the Indian Ocean British territory of Diego Garcia, where records about the conditions in which they were held are "woefully inadequate".

In a separate report, the committee said the government has "failed to take action" and there is "no clear policy" for preventing UK complicity in unlawful rendition.

The ISC said the government's failure to ensure the US and other allies cannot use British territory for rendering detainees was "completely unsatisfactory", especially since there has been a "clear shift in focus" of US policy under the Trump administration.

Ken Clarke, chairman of the All-Party Parliamentary Group on Extraordinary Rendition, said the findings of the ISC report "are not small issues which can now be swept under the carpet - and the government must address them urgently".

"The APPG has been working on these important issues since 2005 and it is more crucial than ever today to finally get to the full truth."

Mr Clarke added: "The ISC says 'we find it astonishing that, given the intense focus on this issue 10 years ago, the government has failed to take action.' I strongly agree."

Human rights campaign group Reprieve has called for a judge-led inquiry, saying the ISC's report was too limited.

Baroness Chakrabarti, Labour's shadow attorney general, echoed calls for a separate inquiry.

She said: "In the days, months and years after 9/11 there was an understandable febrile atmosphere and the senior partner in the special relationship, i.e. the United States, was dabbling in these most horrific practices and - to some extent - the UK government went along for the ride."