It is illegal to tow a vehicle on the public road without an MoT unless you are taking it to a pre-booked MoT test or pre-booked repairs, so if you were repairing the vehicle at home this is a potential grey area where you could be prosecuted if stopped by the police. Your insurance may also be invalid if you are using a car on the road without a valid MoT. If you can tow the car on a trailer with all four wheels off the ground then this would avoid any legal issues.