The recall of the House of Commons is covered by Standing Order 13 (Standing Orders of the House of Commons - Public Business) - available here.
13.—(1) Whenever the House stands adjourned and it is represented to the Speaker by Her Majesty’s Ministers that the public interest requires that the House should meet at a time earlier than that to which the House stands adjourned, the Speaker, if he is satisfied that the public interest does so require, may give notice that, being so satisfied, he appoints a time for the House to meet, and the House shall accordingly meet at the time stated in such notice.
(2) The government business to be transacted on the day on which the House shall so meet shall, subject to the publication of notice thereof in the order paper to be circulated on the day on which the House shall so meet, be such as the government may appoint, but subject as aforesaid the House shall transact its business as if it had been duly adjourned to the day on which it shall so meet, and any government order of the day and government notices of motions that may stand on the order book for any day shall be appointed for the day on which the House shall so meet.
(3) In the event of the Speaker being unable to act owing to illness or other cause, the Chairman of Ways and Means, or either Deputy Chairman, shall act in his stead for the purposes of this order.
The recall of the House of Lords is covered by Standing Order 17 (Standing Orders of the House of Commons - Public Business) - available here.
(1) If, during any adjournment of the House, the Lord Speaker, after consultation with Her Majesty’s Government, is satisfied that the public interest requires that the House should meet at a time earlier than that appointed, he may signify that he is so satisfied and notice shall be given and thereupon the House shall meet at the time stated in the notice, as if it had been duly adjourned to that time.
(2) If the Lord Speaker is unable to act for the purposes of this Standing Order, the Chairman of Committees, after consultation with Her Majesty’s Government, may act in his stead.
In the past Parliament has been recalled to discuss the 9/11 terrorist attacks in the USA (2001); Iraq and weapons of mass destruction (2002) and the Falklands War (1982).
The House of Commons will meet at 11.30 for a statement from the Prime Minister on the riots and a second statement on the economy. The Lords will meet at 12.00.
