There is separate legislation governing spending promoting particular candidates at a UK Parliamentary general election.
Under the Representation of the People Act 1983 (RPA), the candidates standing for your party will appoint agents, who are responsible for the candidate’s spending and must report it in a return after the election.
Political parties support their candidates in various ways. This may have to be reported in different ways, depending on what you do. Since often it must be reported by the candidate and agent, this is covered in more detail in the candidate guidance.
If your activity promotes a particular candidate during the candidate regulated period, then it will fall under the RPA in some way.1
The next question is how it must be reported as spending, and who by.