I'm pretty sure the car you're towing needs to be at least 3rd party insured, which means -legally- you'd need to have a valid MOT certificate. It'd be sods law that a copper would be sitting there, see you towing a rusty old golf and do a spot check.
Makes sense really I suppose, even though the engine isn't running its just as likely to have an accident. Not what you wanted to hear I'm sure, but better to know now then get taken to court
