Tony Blair needs his Cabinet as much as they need him

The sole circumstances under which Blair has truly prime ministerial power would last three minutes

IMAGINE BRITAIN under nuclear attack. Only one man - or woman - can authorise the Chief of Defence Staff to give the order for the retaliatory launch of Trident Cruise missiles: the Prime Minister. Nothing surprising here, except that, apart from hiring and firing his ministers, it is more or less the only executive action which a prime minister is entrusted by the constitution to carry out on his own. The sole circumstances under which he has truly prime ministerial power would have three minutes to last.

This graphic point is made by Professor Peter Hennessy to illustrate the formal limits of the prime minister's executive authority in the British system. Unlike the secretaries of state, who have a host of statutory powers, duties and discretions, he has none. Never mind that he has many fewer formal powers than Jacques Chirac or Boris Yeltsin or Bill Clinton; he cannot even issue a circular to local education authorities as David Blunkett can.

As Jack Straw, the Home Secretary, points out in this week's programme in the BBC Radio Four series Matrix of Power, an individual secretary of state's authority rests partly on the fact that his or her name, and not the prime minister's, is on the big Bills going through Parliament. On the face of it, of course, this seems a mere technical point.

If ever there was a time when a prime minister can order his ministers to do more or less what he wants them to, it is now. His popularity, his authority in his party, his media image of sheer indispensability all make him a frighteningly formidable adversary for a Cabinet dissident. His power may be informal; but that doesn't make it any less real.

At present the idea of loose, collegiate, Cabinet government a la John Major or Jim Callaghan could not seem more remote. There is precious little sign of the full-scale internal debate within the Cabinet which feature on the pages of the Crossman or the Barbara Castle diaries. Ministers across the political spectrum frequently attest to the degree of ideological unity in government.

Further, the recent reforms to the Cabinet office by Sir Richard Wilson, the Cabinet Secretary, were widely seen as strengthening the grip of the centre on the departmental baronies - even to the extent that some officials have even suggested that they will help to usher in a more "Napoleonic" system of government. The "kitchen cabinet" of the unelected advisers to both the Prime Minister and to some extent the Chancellor of the Exchequer, seem more powerful than most junior or middle ranking Cabinet ministers.

A strong prime minister can indeed wield huge authority over his Cabinet colleagues, even on a policy issue in which he or she is facing strong opposition. The immediate trigger for Michael Heseltine's resignation from the Cabinet over Westland in 1986 was Margaret Thatcher's refusal to risk a debate on the issue in the full Cabinet after losing the argument in a Cabinet committee.

But Mr Heseltine says in the programme that he thinks she would probably have won if it had been debated by the full Cabinet. The subsequent experience of the poll tax suggests that he is right. Privately almost all the Cabinet had severe doubts about the wisdom of the Community Charge.

Yet no minister was prepared to support Nigel Lawson in his opposition to Margaret Thatcher over it. As Lawson notes in his memoirs, ministers are primarily interested in their own departmental battles: "When an issue arises where the prime minister of the day and the responsible minister are wholly at one,their colleagues - who have causes of their own over which they are seeking either prime ministerial support or resisting prime ministerial pressure - are disinclined to raise objections."

Professor Hennessy's point nevertheless goes to the heart of a peculiarity in the British system. The organic chemistry of a British Cabinet, even one as visibly dominated by its Prime Minister as this one is, is more subtly balanced than it looks.

First, as Lawson's remark implies, it is much more difficult for even strong prime ministers to get their way if the relevant departmental minister is opposed to the policy. Margaret Thatcher was unable to overcome the Energy Secretary Peter Walker's resistance to breaking up British Gas when it was privatised.

It is interesting to speculate over what would have happened had David Blunkett mounted all-out resistance, say, to the reappointment of Chris Woodhead as Chief Inspector of Schools. He might have used up a lot of credit in the prime ministerial bank. But would Tony Blair have been prepared to risk his resignation on the issue?

Second, all prime ministers are circumscribed by the independent power of the Chancellor, at least on matters, which directly affect the economy. A prime minister, for example, who allows a Chancellor to resign because he wanted to be too prudent is taking a huge gamble.

When Harold Macmillan described the resignation of Peter Thorneycroft in 1958 as a "little local diffculty" - in the days when prime ministers did their own spinning - he was in fact deflecting a grave threat to the government's economic credibility.

That's one reason why strong Chancellors tend to win their arguments over curbs on public spending - as John Major discovered in at least one Cabinet defeat over education spending at the hands of Kenneth Clarke, and as even Tony Blair has had to recognise on occasions over NHS funding.

Finally, while the right to sack and force resignations enjoyed by the prime minister is a hugely potent source of authority, there are limits to the extent that it can be wielded without collateral damage to his own office - as Margaret Thatcher discovered.

Oddly the correlation between the prime minister's strength of personality and the collegiate nature of Cabinet government is less inverse than you might think. As a peacetime Prime Minister, Churchill was actually a romantic about Cabinet between 1951 and 1955, bringing most issues to full meetings and allowing himself to be contained by them on occasions, for example on relations with the Soviet Union.

No prime minister, however powerful, can affiord to ignore his Cabinet permanently. He may not need them now but sooner or later he will. Indeed the more he consults them when he doesn't have to, the more they will show understanding when he can't. Tony Blair shows signs of recognising this. It is one of the reasons, no doubt, that the Prime Minister recently held an "away day" for the Cabinet at Chequers to discuss the government's strategy and policy in the months and years ahead - with the promise of more to come.

In the British system, Cabinet ministers remain, as Douglas Hurd calls them, the "big beasts of the jungle". Cabinet government may be in its dormant phase, as it seemed to be when it was written off before at times under Lloyd George, or Margaret Thatcher. But it will come back.

Donald Macintyre will present a programme on the Cabinet in the current BBC Radio Four series `The Matrix of Power' to be broadcast this Thursday at 8.30pm