my ex still has a key

[biscuitboy]

if they go in my house without permission can they be arrested?

[Ethel]

Is he still on the mortgage/deeds/rent book?

You could always change the locks.

[##Wardy##]

You can be arrested for any offence nowadays if certain criteria is met. If this relates to "domestic issues" then yes he can be arrested even for civil trespass.

The problem is though whether there will be an actual offence.

Does he have implied permission or has it been withdrawn? And, further is he aware of this? This will be the key (no pun intended).

Also would this action be reasonable to collect his own possessions?

I assume there is no injuction or harrasment laws etc governing this.

My advice, change the locks pronto.