File Photo: Members of the Islamic State militant group. (Associate Press)

Britain's special forces have reportedly been given "carte blanche" to launch raids inside IS-held territory and direct airstrikes to kill or capture terrorist leaders who pose a threat to the UK.The elite Special Air Service (SAS) and Special Boat Service (SBS) will be working with the MI6 spy agency and GCHQ, the UK government's eavesdropping service, to pursue Islamic State (IS) and other terror groups, 'The Sunday Times' reported.The move is understood to be the "tip of the spear" of Prime Minister David Cameron's "broad spectrum" approach to combating IS after the Tunisia beach massacre that killed 30 British tourists.Britain's special forces are to be placed on a proactive rather than reactive footing, which means they will be given a green light to attack terrorist networks that pose a credible threat to the UK, the newspaper reported.This could see special forces carrying out so-called strike missions anytime and anywhere but in reality the area of operation is likely to be Iraq, Syria and north Africa.A force of between 60 and 100 members is expected to be committed to the mission, which will involve elite British troops working alongside US Delta Force and Navy SEALs.The troops will be involved in target identification for airstrikes in both Iraq and Syria, battle damage assessment and strike operations against "high value targets" such as regional leaders of IS.The troops will also co-ordinate Reaper drone attacks against IS targets. MI6, which has established a sizeable network of agents within the jihadist group, and GCHQ will provide the intelligence for the missions.The operations will be planned and coordinated by permanent joint headquarters in Northwood, London.Sources told the 'Sunday Times' each mission will probably require the approval of the prime minister.