What is prime minister's questions?

A prime minister has to think on his feet to answer MPs

Prime Minister's Questions or "PMQs" is a high point of the parliamentary week.

Each week on Wednesday afternoon the prime minister must come to the House of Commons to answer oral questions for half an hour.

This system was changed by the current Labour government shortly after they came to power in May 1997. Previously PMQs took place on Tuesday and Thursday afternoons for 15 minutes.

The leader of the opposition may make up to six interventions (previously three) during PMQ's and the leader of the Liberal Democrats will normally ask two questions (previously one).

This change has prompted much debate.

The biggest fireworks come when the Opposition leader speaks

At the time of the change the Conservatives opposed the move saying it reduced the number of times the prime minister was forced to account for his actions in Parliament.

But the government argues that it gives backbench MPs more opportunity to question the prime minister in depth, rather than for a relatively short session.

Prime Minister's Questions follows a different format to those of questions to other ministers. MPs do not normally give the prime minister prior notice of the subject which they are going to raise.

This element of surprise allows opposition MPs, in particular, to try to catch the prime minister out with an awkward question. The prime minister must respond without delay, thinking on his or her feet.

Government backbenchers can normally be relied upon to ask a "helpful" question which will allow the prime minister to tell the House about successful government policies.

The relative performance of each of the main party leaders is closely watched and each is under great pressure to get the better of their opponent.

The chance to ask the prime minister a question is highly prized. The names of the MPs who will get the chance to ask the prime minister a question are drawn in a weekly lottery.