British Prime Minister Theresa May leaves 10 Downing Street in London. Credit:AP There was no official response to the report, which comes hours after police said they had charged two men with terrorist offences. Naa'imur Zakariyah Rahman, 20, and Mohammed Aqib Imran, 21, were arrested in raids by counter-terrorism police last week and are due to appear in a London court on Wednesday. The news came as an independent review of British police and intelligence services found the attack on the Ariana Grande concert at Manchester Arena in May could have been stopped. MI5 missed two clues to the attack that killed 22 people, including that 22-year-old Salman Abedi was planning an attack, and a "data-washing exercise" had identified the attacker as meriting further investigation. MI5 had planned to discuss his case but the meeting was scheduled for nine days after the attack took place.

The review also confirmed that the leader of the June London Bridge and Borough Market attack had been identified as wanting to attack the UK, and was under investigation at the time. He was the main target of a police operation which had been suspended twice because of a lack of resources, and had resumed just before the terror attack. David Anderson, QC, at the request of home secretary Amber Rudd, assessed nine classified internal reviews conducted by MI5 and Counter-Terrorism Policing. He said the "fundamentals are sound" at the police counter-terror command and MI5, and "in a free society and against a worsening threat background, it is not realistic to expect everything to be stopped". However, three of the six attackers had been on MI5's radar, either as an active subject of interest (Khuram Butt, who led the London Bridge attack) or as closed subjects of interest (Khalid Masood on Westminster Bridge and Salman Abedi in Manchester).

"It is conceivable that the Manchester attack in particular might have been averted had the cards fallen differently," Anderson said. He endorsed the 126 recommendations that emerged from the internal reviews, which included wider sharing of information from MI5 intelligence, including with neighbourhood police. In response to his 61-page report, Amber Rudd said the blame for the attacks "lies squarely" with the terrorists. This year saw four terror attacks in England: In March, Khalid Masood, 52, drove a 4WD into pedestrians on Westminster Bridge then fatally stabbed a police officer guarding parliament, leaving 6 dead including the attacker.In May, 22-year-old British-born Salman Abedi set off a home-made bomb in the foyer of an Ariana Grande concert at Manchester Arena, killing 22 people as well as himself.In early June, three men led by 27-year-old Khuram Butt drove a van into pedestrians on London Bridge, killing two people, then ran through Borough Market killing six more people before armed police shot them down. 45 people required hospital treatment. Later in June, 47-year-old Darren Osborne drove a van into a crowd of worshippers outside the Finsbury Park mosque. One man died, and Osborne has been charged with murder.

The report found that Masood was known to police for violent offences and to MI5 for association with extremists. However his file was closed at the time of the attack, no intelligence was being gathered on him and neither MI5 nor the police had any reason to anticipate the attack. He came onto MI5's radar through links to a terror group that had been planning to make home-made bombs, and another group who had sought to travel to Pakistan to train with al-Qaida. However the links were tenuous and no information suggested he was planning an attack. In 2013, he was known to have said he was happy that the September 11 attack had attracted people to Islam, however it wasn't thought enough to reopen his file. There was no clue that he was planning an attack himself until a few minutes before the attack, when he shared his jihad document with his WhatsApp contacts. Salman Abedi, too, had been under MI5 investigation due to suspected contact with a Islamic State figure in Libya, but after investigation his file was then closed.

However twice in the months prior to the attack, the report said, MI5 received intelligence that "can be seen to have been highly relevant to the planned attack". Unfortunately the significance was not fully appreciated at the time, and was assessed as non-terror related. A computer "data-washing" system had also identified Abedi as one of a small number of individuals meriting further examination, but MI5 did not get round to discussing the case before he attacked Manchester Arena. In their review, the intelligence service concluded it was unlikely they would have been able to pre-empt the plot, however they did miss an opportunity to set a 'ports alert' so he could have been questioned and searched when he returned from Libya just before the attack. Khuram Butt was the subject of a live MI5 investigation dubbed Operation Hawthorn, opened in mid-2015 following information suggesting he wanted to conduct a terror attack in the UK. MI5 graded him "high risk" and he was under surveillance but it did not reveal his plans, the report said, and he was downgraded to "medium risk" in late 2015.

Operation Hawthorn was put on hold for a time in early 2016, because of resourcing limitations in the wake of the Bataclan attack in Paris. It was suspended again in March 2017, and MI5 were uncertain whether he posed a threat. They reopened the operation in May, to assess whether it should be closed altogether. The report said Butt "displayed strong operational security" and even today much remains unknown about he and his co-conspirators' plans. Home secretary Amber Rudd presented the report to parliament, and said it was essential to examine what happened to maximise the chance it would not happen again. "Taken as a whole, MI5 and CT Policing conclude they could not find any key moments where different decisions would have made it likely that they could have stopped any of the attacks," she said. However there needed to be a concerted effort to improve MI5 and the police's ability to use data to detect activity of concern.

Loading And MI5 and police will pilot new programs to share intelligence with local authorities. with Telegraph, London; Agencies