French police have arrested 150 illegal migrants near Calais, in an operation targeting a sprawling tent city of people hoping to travel secretly to the UK.Hundreds of migrants live in makeshift tents in the woods near the northern French port as they wait for their chance to board a lorry and cross the Channel. French officials say the three hour dawn raid was aimed at cutting off people trafficking networks. Those arrested are said to be mainly from Afghanistan, Iraq and Eritrea. They are being held for questioning at police stations in Calais, Boulogne and Lille. The raid comes two days before a visit to Calais by the French Immigration Minister, Eric Besson.