The Government does not know how long the Armed Forces will be engaged in Libya, a defence minister admitted as debate intensified over the likely outcome, cost and leadership of the mission. Nick Harvey, the Armed Forces minister, was asked how long Britain would be involved in the military operation in north Africa. He replied: “How long is a piece of string? We don’t know how long this is going to go on for.” His admission, three days into the intervention, came as ministers faced mounting pressure to set out the limits of Britain’s involvement and explain their eventual exit...