For everyone screaming at the OP to get legal advice, just take a breath.
She posted just after 4pm yesterday (Monday) seeking advice before she took legal advice. It appears she has done her homework because she’s on top of the Torts available, the difference between a car on her property as opposed to a sofa.
Presumably she wants to instruct a solicitor to say, under this legislation/civil process please begin proceedings. I would expect this is so she doesn’t waste hours of a solicitor’s time being told what she can and can’t do.
And PPs are screaming at her to get legal advice. Well, she emailed a solicitor this morning before 9am. What would you expect between 4pm yesterday and 9am this morning?
And then there are the intrusive questions: tell us the make and model, (which could be very identifying), did you inherit your house, how old are you and your relative - all of which are irrelevant to her query.
Then there are the unhelpful suggestions to just dump it in the road, or deliver it to her relative’s address. The OP has very clearly (and calmly in my view) said, I want to sell my house, my relative’s car is on my property, they won’t move it voluntarily, how do I get the car moved to their property legally before I put my house on the market.
Then there are suggestions she’s being dramatic. She’s not dramatic, she’s at the end of her tether, trying to resolve a problem and asking for our help and support.
Lay off her. She’s doing her best, and her life is not entertainment for MN posters.