London - The deadly suicide bombing at Manchester Arena might have been prevented if information had been handled differently, an independent review of the counter-terrorism performance by British police and intelligence services suggested on Tuesday.
The review by lawyer David Anderson, ordered by Home Secretary Amber Rudd, said the 22 May attack that killed 22 people might have been thwarted "had the cards fallen differently".
He also found that three extremists involved in four attacks in Britain earlier this year had at some point been investigated by counter-terrorism police or security services.
Nonetheless, he credits police and the MI5 domestic intelligence service with stopping most attacks at a time when Britain faces an unprecedented level of extremist activity.
"MI5 and counter-terrorism policing got a great deal right — particularly in the case of Manchester, they could have succeeded had the cards fallen differently," Anderson said.
Some of these details had been known before, but Anderson raised the tantalising prospect that MI5 might have been able to prevent the most lethal atrocity — the concert attack — had it handled information differently.
Greater Manchester Police Chief Ian Hopkins, Metropolitan Police Commissioner Cressida Dick and other officials said they welcomed Anderson's report.
London Mayor Sadiq Khan, however, said major funding cuts to London police imposed by the central government must be addressed.
"The government must urgently agree to real terms increases in police funding over the coming years if we are to maintain officer numbers and keep the public safe," Khan said.
The reports says Manchester bomber Salman Abedi wasn't being actively investigated when he detonated a suicide device, although he had been scrutinised in the past as a "subject of interest".
But Anderson says MI5 obtained intelligence in the months before the attack that might have led to an active investigation of Abedi "had its true significance been properly understood".
The report says two pieces of information came to MI5 indicating possible criminal activity by Abedi, but this wasn't judged to be related to possible terrorist acts.
"In retrospect, the intelligence can be seen to have been highly relevant to the planned attack," Anderson said.
He also found that counterterrorism officials didn't place a so-called ports action on Abedi after he travelled to Libya in April. That was a missed opportunity, the report says.
"This would have triggered an alert when he returned shortly before the attack, which could have enabled him to be questioned and searched at the airport," Anderson said.
Anderson said it's not clear whether such an investigation would have led to Abedi's plan being prevented and that MI5 believes it wouldn't have thwarted the bomber.
The bombing happened during US singer Ariana Grande's performance.