Police officers, soldiers, emergency services and intelligence officials took part in London's largest counter-terrorism exercise to date. The simulation of a terror attack has been six months in the planning and codenamed ‘Strong Tower’. It involved 1,000 police across the capital during Tuesday and Wednesday and has tested responses to extremists using firearms. It comes days after 38 people were killed by a gunman in Tunisia, the majority of them British holidaymakers. The Metropolitan Police says this week's exercise is not based on any specific intelligence and is part of a long-term strategy of planning and preparing for all possible types of terror attack. The threat level for terrorism had been raised over the last year, making it vital ‘that we train and we learn’. The reason we have exercises like these is because the police and government are concerned that there are people planning terrorist events.