A new report from the thinktank Demos will put the cat among the pigeons - the centre-left group says that splitting the Home Office in two could actually damage the UK's security.
John Reid wants to divide his current Whitehall fiefdom into a ministry of justice and a security department.
The proposal is under discussion by cabinet colleagues, but today's report warned it could worsen an already "overly fragmented approach to security".
The report, written by Demos lead security researcher Charlie Edwards, concluded: "Managing national security without a strategy is like running an orchestra without a musical score: a recipe for an ill-co-ordinated and out-of-tune response."
It said the lack of an overall plan caused "infighting between departments, mixed messages from politicians and the duplication of resources".
Instead, Demos calls for a "national security strategy" which would be debated by parliament and updated annually on its implementation as well as scrutinising it through a select committee.
And it said a single counter-terrorism budget and a separate fund for policy development could be needed.
