“specifically, one standard which is clear Halacha, which no-one in the Shul can claim to have a Heter for”
Can you elaborate? Many “clear Halachos” are not as clear as they are made out to be. Additionally, I’m not sure what the issue is for the men – if there is a proper Mechitza they can’t see the women during davening anyways, and in the street, these women are no worse than anyone else the men will see.
I understand that you are looking for a solution to the problem, not discussions as to whether or not it’s your job to police the problem, but unless we have more information, it is impossible to ascertain whether it is actually a problem.