Lord Butler has declared himself "horrified" at the spread of informal procedures at Number 10 since he left in 1998.

The former Cabinet secretary is currently conducting an inquiry into the role of the intelligence services in the run-up to the war in Iraq.

He is said to be dismayed by the lack of minute-taking and the absence of a decision-making structure.

Whitehall sources are already speculating that this will lead to a more damning verdict on the government's behaviour than Downing Street may have originally supposed.