Political campaigning is not allowed near or inside polling stations during voting for any type of UK election. The Electoral Commission is the body that governs conduct at polling stations. While it issues guidance rather than law, officers at polling stations are backed up by the police who will take action if voting is being disrupted in any way, including by overt campaigning. However, representatives of political parties can take up positions at the entrance to polling stations. These individuals are called tellers and their purpose is to check that their party's supporters have voted.
Stay outside the polling station if you are a teller. Only one teller is allowed for each candidate and they can only enter the polling station to cast their own vote, to help a voter with disabilities or to cast a proxy vote. While acting as a teller you must not be able to see or hear what is going on the polling station.
Obey instructions from the polling station officers. Do not obstruct or intimidate voters in any way as they enter and leave the station. You can ask electors for their polling card, but not for any other information. Tellers must not say anything to voters that could be construed as political campaigning.
Avoid displaying any campaign material when you are acting as a teller. Tellers are allowed to wear a rosette declaring their political affiliations, but it must be of a reasonable size and must not include a political slogan.
The presiding officer, the person in charge of the polling station, is instructed to check that tellers are obeying the rules.
Any polling cards collected by a teller must be handed to polling station officials when voting is over.