When Parliament is dissolved every Commons seat becomes vacant and there is a general election. Below is the expected timetable published ahead of the 2010 General Election, setting out the timescales of the campaign and what was to happen after polling day when the new MPs take their seats and Members of the Lords return.
Tuesday 6 April - General Election announced
The Prime Minister goes to Buckingham Palace to ask the Queen to dissolve Parliament on the following Monday 12 April
From Tuesday 6 April - Wash-up and Royal Assent
While Bills can be carried forward from one parliamentary session to the next, the same cannot happen between parliaments. All Bills not passed on the date the House rises are lost.
Parliament has evolved a mechanism called the "wash-up" whereby some Bills are saved and allowed to complete their passage.
Both Houses of Parliament continue to sit until the Parliament is formally dissolved on Monday 12 April.
Bills receive Royal Assent when they have completed their passage through Parliament
Thursday 8 April - Prorogation
The formal end of the parliamentary session is marked by what is known as prorogation. Dissolution is on Monday 12 April.
Monday 12 April - Dissolution
A proclamation of dissolution is made, announcing when Parliament will meet after the general election and setting the date of the Queen's Speech at State Opening
Writs issued for elections in the UK's 650 constituencies
Tuesday 20 April
Cut-off date for UK citizens aged 18 and over to register to vote in the general election
Also marks the deadline for voters to apply for a postal or a proxy vote
Candidates' nomination papers must be delivered to the local returning officer. Any candidate wishing to withdraw must do so on this date
Election agents, who ensure the proper management of each candidate's campaign, must also be appointed
Thursday 6 May - Election day
Polling booths open between 7am and 10pm. Counting of votes will begin when the polls close.
Friday 7 May
Tuesday 18 May
Commons to choose the Speaker of the House of Commons
MPs start swearing the Oath of Allegiance or making an Affirmation in the Commons
Members of the House of Lords start swearing the Oath of Allegiance or making an Affirmation in the Lords
Tuesday 25 May
The Queen's Speech is delivered at the State Opening of the new Parliament.