Leading article: Spooked by MI5? There's no alternative at the Olympics

Security was always going to have to be a priority at the London Olympics, but the terrorist killing spree in France last week puts even more pressure on the intelligence services.

The lessons from Toulouse are far from encouraging. Islamist fanatic Mohamed Merah, who was killed in a shootout with police on Friday, appears to have been a "lone wolf". Although French intelligence had kept tabs on him for years, his horrific attacks were not planned with the help of any terrorist networks, and were therefore impossible to predict.

Against such a background, it is some comfort that MI5 will be mobilising all possible resources for the Olympics, launching its biggest single operation since the Second World War. And although it may be disquieting for a warship to be anchored in the Thames Estuary and the capital to be ringed by surface-to-air missiles, there is – unfortunately – no alternative.