Britain's most senior generals have issued a blunt warning to Downing Street that the military campaign in Afghanistan is facing a catastrophic failure, a development that could lead to an Islamist government seizing power in neighbouring Pakistan.

'The consequences of failure in Afghanistan are far greater than in Iraq,' he said. 'If we fail in Afghanistan then Pakistan goes down. The security problems for Britain would be massively multiplied. I think you could not then stop a widening regional war that would start off in warlordism but it would become essentially a war in the end between Sunni and Shia right across the Middle East.'