There is no legal form as such and it sounds as if what you should do is write to him giving notice that unless he removes any items belonging to him within 14 days, you will consider them abandoned and dispose of them.
Click on any Q to read the answer.
• Get a divorce
• Have contact with my children
• Make a small claim
•Write a letter of claim
•Obtain a Grant of Probate
•Get legal advice and help with my case
•Make a Will
•Change my Name
•Prepare a legally binding agreement
• Sever a Joint tenancy
• Prepare a Partnership Agreement
• Sell a Jointly owned Property
• Appoint a Guardian for my children