If MI5 made mistakes, we need to know Two images emerged yesterday that could not have been more different. One was of the street in Woolwich where people have laid a "wall of flowers" in memory of the murdered soldier, Drummer Lee Rigby. The second was a photo of David and Samantha Cameron on holiday in Ibiza, many miles removed from the tragedy at home. We have always stated that prime ministers have a need and a right to take holidays. But the photos of Mr Cameron's vacation were sorely misjudged. They call into question, once more, his political sensitivity. A smarter move was his announcement of the formation of a new counter-extremism task force that will "look again" at the Government's strategy for tackling radicalisation. And look again, it must - for there are many troubling questions about the death of Drummer Rigby that our security forces have to answer. It is true that MI5 has prevented many terrorist attacks from taking place on British soil. It is also true that it is hard to stop "lone wolf" terrorists - those who act spontaneously and without the support of a wider network. MI5"s defenders point out that its resources are limited and it cannot always carry out surveillance on those who operate only on the periphery of Islamic radicalism. But Theresa May, the Home Secretary, said yesterday that the attack in Woolwich was more than a lone wolf incident. One of the suspects, Michael Adebolajo, was arrested in Kenya in 2010, accused of trying to join an affiliate of al-Qaeda - and subsequently deported to the UK. A friend has also claimed that Adebolajo was approached by MI5 to work for the security service. Meanwhile, the other suspect, Michael Adebowale, was detained by police two months ago after shopkeepers complained about a group of Muslim extremists. It is difficult to understand why MI5 did not maintain tighter surveillance on a man like Adebolajo, who joined Islamist protests and was known to radical preachers. Worse still, this is an apparent repeat of an old, deadly mistake. One of the bombers involved in the July 7 2005 attacks in London was also known to MI5 but had been dropped from surveillance because he had not been thought a serious risk to national security. We agree with Lord Blair, the former commissioner of the Metropolitan Police, when he noted last week that it took four long years to find out what went wrong in 2005 and that the Government must "act fast" to examine and acknowledge any mistakes that were made this time. After Woolwich, we need speedy assurance that our security services are operating correctly.