dealers can de-register a new car if the sale falls through https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1051137/v996-application-for-de-registration.pdf
The dealer would have to contact the orignal buyer which the vehicles VIN and registration was attached to and request a letter with this information including their full name and address, comfirmation and why the sale didn’t go through. Would an angry peeved customer do this if they didn’t get the car they ordered?