My Lords, I pay tribute to the noble Lord’s knowledge and experience in this area. He will know that policing requirements are assessed almost day by day, and a particular situation may well require more armed police officers to be stationed in particular locations. I cannot generalise about that, but I am sure that noble Lords will all be conscious that the Palace of Westminster has seen a much tighter degree of security from armed police in recent months, for which we should be grateful.
On the noble Lord’s general point, I agree. Surveillance is important but, as David Anderson himself acknowledges, it is impossible for the authorities to prevent every single terrorist attack. In his executive summary he says in terms that the recommendations, if accepted, would not remove the risk of a terrorist attack—to do so would be manifestly impossible in a free society. He also mentions that MI5 and CT policing have thwarted 20 Islamist terrorist plots in the past four years, resulting in 10 life sentences from the seven plots that have so far come to trial. So we can point to some signal successes achieved by MI5 and the police, but they cannot possibly be expected to pick up lone-wolf attackers.