If he is damaging things then it’s a matter for the police. Criminal damage.
Your friend would be perfectly entitled to simply lock the boyfriend out provided he doesn’t pay rent.
If she does that and he becomes troublesome, call the police. 999.
It is the marital home and she is free to come and go as she wishes and she has as much right as her husband does even though the property may not be in her name. The boyfriend clearly needs to take better legal advice
Your friends can call the police if he will not leave and they may or may not get involved. They shouldn’t get involved to be frank because this is not a criminal matter except with regard to the damage although you can get them to attend is likely to start being very awkward which is not going to do him any good.
She could tell him that if he does not agree now, this minute, to leave by 6 PM, she is going to call the police now with a view to having him prosecuted for criminal damage in respect of the car and the cupboard and anything else.
Thank you for letting me assist you with your legal question. I am glad that I was able to help.
I am not certain whether that answers the question for you or not, but I am happy to answer any specific points arising from this.
It will be my pleasure to help you again either further with this or any future questions you have