I don't agree with filling in any of the docks but I think you attach too much importance to the World Heritage status afforded by UNESCO.
This is nothing but a hollow title dubiously awarded by a discredited organisation (the UN) who are treated with open contempt or totally ignored in matters of international importance by all of the world's major players.
I think the planning route is the way to go on this.
It seems quite obvious that the rules and regs are being ignored or flouted, both at a local and national level, by those entrusted with enforcing them.
What can you do though when the ODPM, the ultimate body charged with making planning decisions, ignores all of its own advice and regulations to allow a football stadium to be built in a public park?
Why should anyone follow any laws if central government can't even stick to their own?