It was business as usual on London Underground’s newly re-opened Picadilly Line on Thursday morning, except for one detail.More than 6,000 police officers are patrolling stations and the streets, some of them are armed. Police say there has been no specific intelligence but London is on a very high state of alert, four weeks to the day after the attacks that killed 56 people including four bombers. Following the deadly strikes on three tube trains and a bus – and the failed attacks two weeks later – tube passenger numbers are down by up to 30 percent. The police operation is said to be costing an extra 750,000 euros a day, but it is keeping the visitors coming. One Antipodean tourist said: “It’s probably safer now.” Another from Canada said: “We knew before we came, we knew that our hotel would be close to a station that had had problems. But that never stopped us thinking about our holiday. We thought ‘We’re gonna go’ and London people have been great.” Police believe all four men they were hunting over the failed July 21 bombings on three underground trains and a bus are now in custody. A 23-year-old man was due to appear in court on Thursday, charged with hindering the investigation into the failed attacks by protecting a possible suspect.