Planning application-related bullying - what can be done, if anything?

[FatherReboolaConundrum]

A planning application in a friend's area has attracted a lot of opposition, some of it in the form of a petition. The owners of the property are apparently paying some of the people on the petiton a visit (including my friend) and being aggressive in their demands that the signatories retract their signatures. Does anyone know if this would be regarded as a problem by planning policy? And if it is, who could my friend riase this with?

I would raise it with the planning dept and try to get someone to record these threats/demands on their phone.

Thank you MrsJD, that's a good idea, I'll pass that on. I think they are also going to talk to their local councillor.