Nonetheless, the organisation of counter-terrorism in Whitehall is likely to change, probably after Gordon Brown takes over in the summer. The Reid plan, the latest stage in his eight-month long revamping of the Home Office, consists of dividing the department in two: in effect between pre- and post-arrest.

The former, covering counter-terrorism, police and immigration, would go into a national security department, and the latter, covering prisons and probations (the recently reorganised National Offender Management Service) would be merged with the bulk of the Department for Constitutional Affairs covering the courts and legal aid to form a Ministry of Justice.

The public reaction from 10 Downing Street is that this is a serious suggestion that requires full consideration by the Government as a whole. In private, however, senior ministers and officials were annoyed by the floating of the plan in the Sunday newspapers in what is seen as an attempt at headline-grabbing by Mr Reid and his advisers on a proposal that had not been properly discussed within either the Home Office or the Cabinet.

It is hard to find anyone at a senior level who favours such a split. Recent problems, such as over the release of foreign prisoners, could be made much worse if immigration and prisons were put in separate departments.

The need is, rather, for better co-ordination, not division of ministerial responsibilities, as well as budgetary clashes, which could damage reform of criminal justice. Moreover, officials with international experience point to the problems overseas where counter-terrorism and justice are split. The wide-ranging fight against terrorism cannot be concentrated in just one department.

The difficulties at the Home Office are blamed on constant chopping and changing of people and policies. The solution is seen as consistency of objectives.

A more likely option is strengthening the centre. Mr Brown has said that, as part of the Comprehensive Spending Review, the case for a single security budget will be considered again alongside an annual statement on national security strategy. The Prime Minister would be very much in charge.

A variant on this approach was put forward last month by Sir David Omand, the former intelligence and security co-ordinator.

In a speech to the Demos think-tank, he urged a proper national security committee chaired by a senior Cabinet minister, as well as a strong joint assessment and planning staff to pursue such a strategy.

There may also be a forum with senior figures from across the political spectrum, academia and political life.

That would be akin to a prime minister’s department, but the key is fully integrating No 10 with the Cabinet Office serving the full Cabinet, not exactly the current position.

Ideas along these lines are being considered at the top of Whitehall. Mr Brown is also thinking about shifting departmental responsibilities.

Expect an upheaval as profound as that from a previous chancellor-turned-prime minister: Lloyd George.

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