1 Offence of campaigning within a prescribed area
(1) It shall be an offence to engage in campaigning activity within a prescribed area around a polling station on the day of a relevant election at any time during the period in which the polling station is open.
(2) In this Act, “campaigning activity” means—
(a) the promotion or distribution of any literature associated with election candidates, political parties or associated organisations;
(b) the use of audio equipment, whether stationary or mobile, for the propagation of messages relating to an election; or
(c) oral communication for the purpose of eliciting voting intentions or influencing the casting of a vote.
(3) The “prescribed area” referred to in subsection (1) shall be an area represented by a circle with a radius of 250 metres from the main entrance of a polling station.
http://www.publications.parliament.uk/pa/cm200607/cmbills/027/07027.i-i.html