1-Obtain evidence in writing the build is Illegal.
My understanding is even with no BG in place you should be successful in gaining judgement in court. This really is down to the Lawyer as my evidence is from the council which is available to all (for a small fee!)
This is what everyone should do who wants to know what the status of their development is. IE. Is it legal or not / under investigation. Go to the Town Hall. This is how Charlie, Katerina and I found out about the situation at Green Hills.