More than ever, the Speaker must be able to stand up for Parliament

It is, in some respects, the most sacred office in the British constitution. Since 1376 the Commons Speaker has been the frontline defence of Parliament's liberties and privileges against a sometimes overmighty executive.

It is, in some respects, the most sacred office in the British constitution. Since 1376 the Commons Speaker has been the frontline defence of Parliament's liberties and privileges against a sometimes overmighty executive.

And it is easy to forget, because of the ancient ritual by which the Speaker processes in wig and gown to the Chamber at the start of each day's business with mace bearer, chaplain and attendants, that he or she still is just that.

Originally this meant protecting the Commons' rights against the King. The protective words of William Lenthall refusing Charles I when he wanted to arrest five MPs, including John Hampden, in January 1642 still ring true: "May it please your majesty, I have neither eyes to see, nor Tongue to Speak in this Place, but as the House is pleased to direct me, whose servant I am here."

The pressures on the Speaker may be different now, but the principles remain the same; as the presiding officer, he or she represents the Commons in its dealings with the executive - not, provided that he or she is doing the job properly, the other way round.

Betty Boothroyd may have become a cult figure to United States viewers of the C-span channel, but her job is much more than a piece of Merrie England heritage. Most famously an MP has, in order to make a speech, to catch "the Speaker's eye" - once described by a frustrated Stanley Baldwin as "the most elusive organ that nature has ever yet created".

But the Speaker has many other formidable powers, well summed up by Tony Benn when he spoke in support of Ms Boothroyd in 1992: "Apart from keeping order, which is not as difficult as it might appear, the Speaker can allow or disallow parliamentary questions to ministers, and thus expose or protect them; accept or refuse closure motions which can prolong or stop debates; select or reject backbench motions or amendments, and thus deny a minority view in the House from ever being put... permit or deny private notice questions and emergency debates; call or not call individual members; give or withhold precedence to privy councillors, which is the source of much anger...recall the Commons in a recess or in the event of some international crisis; certify a money bill and rule on matters of privilege."

Modern governments can be just as vexed by the Speakers' powers as tyrannical kings. For example, Lord Weatherill came under huge pressure, although himself a Tory, from members of the Thatcher government, to grant fewer private notice questions - the main vehicle by which the Opposition can summon a minister to account for himself in person.

By contrast, George Thomas, a former Labour Welsh secretary and Lord Weatherill's predecessor, was seen by many MPs as too emollient towards the Thatcher administration.

Now, when the standing of the Commons is probably more in doubt than at any other time in modern days, partly because of the powers devolved to the Scottish Parliament and the Welsh Assembly on the one hand, and to Europe on the other, the need for an authoritative, competent speaker to stand up may be at its greatest.

Any modern speaker recognises the basic right of a democratic government to see its business through. Equally however, he or she has to be vigilant - and never more than now, with a Government which has shown little interest in Parliament's historic role as a check on the executive - to see that the business is properly scrutinised and debated; and that its authors, the government of the day, are properly called to account.