Britain must accept that "sooner or later" ground troops and tanks will have to be sent into combat to overcome Isis a former chief of the Armed Forces has said.
Lord Richards said Prime Minister David Cameron had to get the country on a "war footing" and rethink its military strategy to extinguish the threat posed by Isis (Islamic State) militants.
He said that "tanks would have to roll and there's going to have to be boots on the ground", as he took a swipe at the existing approach, describing it as "dribbling, not clouting".
Cameron's strategy against Isis, based on training Iraqi forces and moderate Syrian rebels was "woefully insufficient", Richards said. He made the intervention as the Prime Minister prepared to warn today that the fight against extremism is now the "struggle of our generation".
Cameron was to give a major speech on how he plans to tackle the menace of Islamic extremism after giving the clearest signal yet that Britain will officially join air strikes against targets inside Syria. Cameron said he wanted Britain to "do more" to destroy Isis and hinted he would soon ask Parliament to authorise strikes in Syria, in addition to the British air campaign already under way in Iraq.
His Defence Secretary, Michael Fallon, was today expected to explain to MPs why British pilots embedded with the US military are already flying bombing raids inside the country, despite a clear parliamentary vote against action in Syria.
Speaking on the BBC's Andrew Marr Show, Richards said: "The current strategy won't work in the time I think we've got available. The current strategy is essentially one of equipping and training others to do the hard stuff for us. I think that could work, but the scale of effort going into it is woefully insufficient." He added: "If we really want to get rid of them ... we need to effectively get on a war footing."
Richards said he "utterly agreed" with the Prime Minister that Isis had to be removed, because their self-styled Caliphate was acting as "a lure and an attraction on all those others that may just be tempted to do things that we all abhor".
If the existing strategy, with no British and allied troops on the front line, was not effective within a year, "then I think we need to look at it again", he said. "Properly brought together with proper leadership and proper command and control it is a very doable proposition. But I worry that - what we call in the Army 'dribbling' instead of 'clouting' - if we dribble, which is really rather what we are doing at the moment, it is simply firing up the problem rather than dealing with it." Asked if sooner or later, ground troops would be needed on the front line, he said: "I suspect my bones are telling me that."
However, any escalation of Britain's commitment in Syria is sure to meet resistance. Cameron's indication he wanted Britain to join air strikes in Syria led one senior Tory MP to accuse him of making up his policy "on the hoof".
Julian Lewis, the chairman of the Defence Select Committee, called on the Prime Minister to present a more considered strategy to Parliament.
In his speech on tackling extremism, Cameron would today say in Birmingham that society must first understand what makes extremist ideology so attractive, before it can be defeated.
He was to set out new measures the Government would take over the next five years to try to stop alienated and isolated young people being drawn to the extremists' "sick world view".