That's why ConservativeHome's fulsome analysis today is such an important contribution to the debate. It talks about £100bn of cuts, and this is by no means a fantastical scenario. I suspect Cameron will hope the IMF steps in to force these cuts on Brown as they did on Callaghan, thus saving the Tories the problem of being seen as the initiators of the radical cuts which will be necessary if Britain is to claw its way back to solvency.
The task facing a Conservative government will be not so much running the country as trying to save it. That's why the ConHome analysis makes for essential, if horribly bleak, reading.