I've just spoken with Jody from Enforcements at Lewisham Council. Apparently others have also complained and about a week ago he gave the church notice that they have to remove the signs within 10-14 days, otherwise he will take action against them. He's going over there to see them again today and will tell them to remove the signs. They aren't allowed on a church. Hoorah! Thanks, Lewisham Council. Much appreciated.