Polling takes place on the 17th day (excluding Saturdays, Sundays, Christmas Eve, Christmas Day, Good Friday, bank holidays in any part of the UK and days appointed for public thanksgiving or mourning) following the date of the Proclamation summoning a new Parliament (Representation of the People Act 1983, sch. 1 Pt 1). Counting starts as soon as possible after the polls close at 2200. Hung Parliaments (and the unlikely circumstance of the leader of the party which obtains a majority of seats actually losing his seat) aside, one expects to know who the next PM will be during the course of the night, and the most senior cabinet appointments by the end of the following day.

This election was not precipitated by a government crisis so much as by the imminent expiry of the five year maximum term. Brown's failure to call an election in 2007 meant that he didn't have an opportunity to ride this one out, and was punished accordingly.