LONDON (Reuters) - British spies were complicit in the mistreatment of hundreds of suspected militants by the United States and involved in dozens of cases of their illegal transfer, according to the findings of a committee of lawmakers.

The Intelligence and Security Committee spent several years looking at the actions of British security and intelligence agencies in relation to the handling of detainees overseas following the attacks in the United States on Sept. 11, 2001.

The committee found British intelligence officers were involved in incidents of mistreatment ranging from officers witnessing torture first-hand to passing on intelligence knowing it could be used in illegal interrogations.

“In our view the UK tolerated actions, and took others, that we regard as inexcusable,” the committee said.

It said it was “beyond doubt” that British intelligence knew at an early stage that the United States, its closest security ally, was mistreating detainees.

The findings will raise fresh questions about whether the government should have taken a more independent approach from that of the United States after the Sept. 11 attacks.

The committee did not find any evidence that British intelligence officers directly mistreated or tortured militant suspects.

But the report said it had found 232 cases where British personnel continued to supply questions or intelligence to allies after they knew about suspected mistreatment.

In 198 cases, they received intelligence obtained from detainees who they knew or should have suspected had been mistreated, the committee said.

It also found 28 cases in which intelligence agencies suggested, planned or agreed to rendition operations and three in which they offered to make a financial contribution to conduct a rendition operation.

DIFFERENT NOW?

After 2001, British intelligence officers and members of the armed forces interviewed up to 3,000 detainees who were primarily held by the United States in Afghanistan, Iraq and at the Guantanamo Bay detention facility.

The committee took 50 hours of oral evidence and reviewed 40,000 documents. It rejected the intelligence agencies’ claims that abuse amounted to “isolated incidents” and criticized the chiefs of the intelligence agencies for failing to recognize a “pattern of mistreatment”.

Responding to the reports, a British security official said Britain’s spy agencies had learned tough lessons since the Sept. 11 attacks.

“Today, we do things differently,” said the official, who spoke on condition of anonymity, adding that spies had been under intense pressure from their political masters.

“Our staff were under pressure to deliver intelligence on the threat,” the official said. “The immediate demand, to deliver intelligence to defend against the terrorist threat, became the overriding priority.”

The committee found no “smoking gun” indicating a policy of deliberately overlooking mistreatment, but said intelligence officers may have turned “a blind eye”.

“The agencies were the junior partner with limited influence, and concerned not to upset their U.S. counterparts in case they lost access to intelligence from detainees that might be vital in preventing an attack on the UK,” the committee said.

Prime Minister Theresa May said in a written response to the report that intelligence officers had been working in a challenging environment they were not prepared for.

“It took too long to recognize that guidance and training for staff was inadequate, and too long to understand fully and take appropriate action on the risks arising from our engagement with international partners on detainee issues,” she said.