Lord Richards said political leaders have failed to grasp the scale of response required to take on the extremists in their Iraq and Syria strongholds, and only have a limited time to improve the existing approach.
Asked if he believes that “sooner or later tanks are going to have to roll, there is going to have to be troops on the ground”, he said: “I suspect my bones are telling me that.”
Lord Richards, who retired as chief of the defence staff in July 2013, told BBC1’s Andrew Marr Show that the scale and effort of the push to train up local forces to lead the fight - alongside air strikes - is “woefully insufficient”.
He said: “The current strategy won’t work in the time I think we’ve got available.
“If you really want to get rid of them we need to effectively get on a war footing.”
He went on: “The existing one could be made to work - that is without British and other allied troops right up in the front line - but if it doesn’t, and I would give us about a year to get it right, then I think we need to look at it again.
“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.
“It’s that scale of vision and effort that, as much as their hearts are in the right place, political leaders right around the world have not yet understood is required.”
David Cameron pledged to help America “destroy” self-styled Islamic State (IS) extremists in Syria as he gave his clearest signal yet that UK forces could be asked to join air strikes.
The Prime Minister said he wanted Britain to “step up and do more” if he could secure the approval of Parliament as he prepared to issue a stark warning to home-grown would-be jihadists that IS wanted them as “cannon fodder”.
He will use a speech today to set out what aides said would be “significant” elements of the Government’s strategy to combat the threat from fundamentalist terrorism for the next five years.