One has to go back to 1956 to the ill-fated invasion of the Suez Canal to recall a year when British foreign and security policy has been so ineptly conducted and caused so much division of opinion in the country.

In both Suez and Iraq, parliament was deliberately misled, leading to profound and widespread disillusionment. Not by coincidence, Sir Anthony Eden and Tony Blair also both chose to centralise all decision making in No 10, bypassing the Foreign Office and the Ministry of Defence.

I have wanted Blair to succeed ever since he became the Labour party leader in 1994. I have supported him on every major political issue since then, including Iraq and variable fees for university education. The notable exception has been his enthusiasm to rush into embracing the euro and to adopt the most recent draft of a European constitution, both of which, without much clearer definitions and safeguards, would cut deeply into the UK’s independent governance.

I still believe that toppling Saddam Hussein was the correct policy and I feel that Blair deserves to stay in office long enough for Iraq perhaps to be accepted as an achievement, not a failure.

The possibility undoubtedly exists that the formidable power of the United States will succeed in establishing security on the ground and a viable transitional government within the next six months. It is in one way an advantage that George W Bush faces his re-election in November — so ensuring that he will remain highly focused on achieving a result in Iraq before then.

However, it has the disadvantage for Blair that the domestic political debate in the United States will mean that the controversial issues that have underpinned the whole Iraqi venture — and which have divided public opinion in the UK — will continue to grab headlines on both sides of the Atlantic.

Blair’s political authority has been severely, probably irreparably, damaged over Iraq, not just within his own party but also within the country as a whole.

What is not widely known is that in 2001, after being re-elected, Blair made sweeping changes in the method of conducting foreign and security policy, some of which had been contemplated by Margaret Thatcher but wisely discarded. He brought the European unit from the Cabinet Office, where it had previously co-ordinated departmental responsibilities relating to, first, the European Community and then the European Union, into No 10 as his own European secretariat.

He also created an overseas and defence secretariat, again under his personal control in No 10, drawing in many of the Cabinet Office functions previously supervised by the cabinet secretary.

Today in Whitehall these secretariats are increasingly seen to have failed. This is not the fault of those able diplomats and civil servants who man them. The problem is that the structure within which they work concentrates advice, power and executive control in one person — Blair — as it was designed to do.

What Iraq and the negotiations around the treaty on a new European constitution have shown is that no one person under our parliamentary system of government can handle competently all the myriad issues that fall into this decision-making nexus. Cabinet government and a tradition of bipartisanship on international affairs in times of far greater danger than exist today have hitherto served us pretty well.

What these two No 10 Blair secretariats have demonstrated is that with them he has not been able to persuade the bulk of parliamentary and public opinion on the two vital issues, Iraq and a European constitution, on which they have been tested.

This alone should be enough for Blair to rethink, but when the secretariats have been linked with quite obviously mistaken judgments it is imperative that they are wound down and that responsibility is returned to the cabinet and its subcommittees.