In constitutional theory, parliament is supreme and the executive is merely its handmaiden. In practical politics, the government can generally rely on a majority in the House of Commons to vote for its proposals.

What checks and balances does our constitution have to stop the UK becoming, in Lord Hailsham's famous phrase, an 'elective dictatorship'?

The judiciary and the media

First, of course, there are the courts. In recent years, the judges have fashioned judicial review into a powerful check on the executive.

Although the judges have always insisted that they are not concerned with the decisions taken by ministers - merely the way in which those decisions are taken - governments have long suspected the courts of seeking ways of overturning decisions which they do not happen to like.

Secondly, we have the media. Journalists, however influential, can do little to stop a government that believes it has public opinion on its side.

But the tabloid newspapers have been remarkably effective in forcing from office several ministers whose standards of morality and behaviour they did not consider acceptable.

Constitutional evolution

And finally, there are the constitutional changes mentioned in other sections.

It seems there can now be no major changes to the powers of parliament without approval from the people in a referendum.

With the prospect of proportional representation for elections to the House of Commons, governments may no longer be able to rely on majorities of landslide proportions.

Central government will have much less power when we have a Freedom of Information Act, when the European Convention on Human Rights is incorporated into our domestic legal systems, and when there is devolution to Scotland, Wales and perhaps - to a lesser extent - in London and some of the English regions.

These developments will further restrict the power of government, making it harder for critics to claim that the UK has an over-mighty, over-centralised executive at the heart of its constitution.