misplaced election poster?

Was that your letter in this morning's Metro raising this issue?
 
But posting on private property is littering.

Question: If someone threw a bottle over the wall and I put it in the bin am I in trouble?
 
One would think so but an election poster remains the property and responsibility of the political party.
 
Tell them you binned the poster, but that you've just learnt that the poster remains their property, and would they like to come and fetch it.