The fact that he may be your ex-husband is not relevant.
He is just another person.
You need to go back to the police because since October 2012, squatting in residential property has been a criminal offence. They are just taking the line of least resistance and saying that it is a civil matter.
complaint to a senior officer the chief constable if need be and show them the above page.
It is a civil matter but it is also a criminal matter.
Depending on how he got into the properties, if he broke in, that is criminal damage and is also a police matter.
He doesn’t pay rent and you can simply break into the property (it is in your sole name) when he is not there, change the locks provided you give him his belongings back.
If you are doing that, tell the police that you have been advised to do that, so them this answer, and tell them you are going to do so that your exhusband cannot allege any kind of violence.
If you would rather not have the confrontation, you need to make an application to court for a court order to make him leave the properties. If you asked the court to attach the notice, and if the ex does not move out, he will be arrested.
I am assuming that this is not the former matrimonial home as that does make a difference
Can I clarify anything else for you?
Please rate the service positive. It is an important part of the process by which experts get paid. It does not cost you anything but helps us greatly.