Urgent Questions - described in the Commons as Private Notice Questions until 2002 - can be used by parliamentarians to ask a government minister to come to the House and make a statement on an important issue at short notice.
MPs can apply to the Commons Speaker for permission to ask an Urgent Question in the House that same day.
Similarly, peers can apply to the Lord Speaker to ask a Private Notice Question in the upper chamber (where they have not been renamed).
An application will only be granted if it is judged to be of great public importance, requiring an urgent response from the government.
If it is granted, the relevant government department is informed immediately and the question will be asked at the end of Question Time.
However, since the House of Lords is a self-regulating chamber, peers can collectively overturn the Lord Speaker's decision.