The Electoral Commission (for what good they are) issues guidelines concerning the code of conduct for political parties, candidates, canvassers and campaigners.
An individual may not exert, or attempt to exert, undue influence to persuade or force someone to vote, not to vote, or to vote a certain way. Someone who prevents or deters the voter from freely exercising their right to vote, or attempts to do so, may be found guilty of undue influence.
The following has been received by someone I know (details blanked) and was personally addressed to them, using their Christian name. The first page contained what I consider to be untruthful/contradictory statements, but then what political pamphlet does not. What I find questionable is the second page.