The role of the Speaker

The Speaker protects the rights of MPs

The Speaker is the enforcer of the House of Commons, charged with keeping unruly MPs in line.

The Speaker is responsible for keeping order during debates and making sure the rules of the House are obeyed - tasks requiring charm, a will of steel and the patience of a saint.

Those misbehaving - be it forgetting to turn off their mobile phones, or being in possession of a leaked select committee report - are pulled up with short shrift.

The soon-to-retire incumbent, Betty Boothroyd, undertook such disciplinary tasks in a way so as to ensure those at fault did not transgress again, said the former cabinet minister, Baroness Williams of Crosby.

Responsible for ensuring parliament provides effective scrutiny of the government, Ms Boothroyd has complained about ministers' tendency to use interviews and press conferences rather than the Commons to make policy announcements.

Madam Speaker with Nelson Mandela

The post is held by a senior MP chosen by all members of the Commons, and traditionally alternates between the two main parties.

The Speaker does not take part in debates and only votes if there is a tie and a casting vote is needed.

In keeping with the task of upholding the traditions of the Commons, the post is steeped in ritual.

On state occasions the Speaker dons a richly-adorned robe. Even on sitting days, he or she dresses in a black silk robe and white wig - headgear Ms Boothroyd refused to wear during her eight years in the post.

The position dates from at least 1258, when Peter de Montfort is said to have presided over the "Mad Parliament" held at Oxford.

The Speaker defends of the independence of the Commons, and speaks formally for the House in its dealings with the Monarch.

In 1642, when Charles I tried to arrest five MPs for treason, Speaker Lenthall stood up for the independence of the Commons.

"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."