LONDON (NYTIMES) - A damning parliamentary report released on Thursday (Nov 22) raised questions about the way Britain tracked terrorism suspects, accusing the authorities of moving too slowly to forestall one of five major Islamist attacks in 2017 and finding a "litany of errors" in the handling of another.

The report by the cross-party Intelligence and Security Committee, titled The 2017 Attacks: What Needs To Change? offered an unusual admission by MI5, the domestic security service, that it had made a mistake in not tracking the Manchester bombing suspect.

The report also offered a sharp counterpoint overall to the portrait offered by security and policing agencies of their successes in foiling terrorist plots.

The conspiracies have proliferated since July 7, 2005, when suicide bombers killed 52 train and bus travellers in London.

The parliamentary report drew some broad conclusions, saying police and the security services were not sharing information as efficiently as they should and criticising official efforts to persuade big technology companies to remove extremist material from their platforms.

Such is the scale of the challenge to fight terrorism, the authorities say, that 700 investigations are underway into some 3,000 suspects regarded as a serious threat, along with an additional 20,000 considered to cause concern.

The police and MI5 say that they have thwarted 13 plots since March 2017, but the parliamentary panel focused on five attacks last year that claimed the lives of 36 victims.

The bloodiest of the attacks occurred May 22, 2017, when Salman Abedi, a 22-year-old Briton of Libyan descent, blew himself up at a concert by pop star Ariana Grande in the north-western city of Manchester, killing 22 people, including several children.

Abedi had been known to the authorities because he had visited a jailed extremist in prison and had travelled to Libya from 2011 onward, the report said. But in 2015, the authorities judged him as posing a low risk.

Mr Sajid Javid, the Home Secretary, who has political authority over MI5, said the security services had updated their counter-terrorism strategy and were "ensuring technology companies play their part by stopping terrorists from exploiting their platforms".

But the parliamentary panel said it was "striking how many of the issues, which arose in relation to the 2017 terrorist attacks, have been previously raised by this committee".

"We have previously made recommendations in all these areas and yet the government failed to act on them," it added.