Driving an unsafe car is a bad idea, regardless of the legal implications. You would be best advised to make sure it is properly safe before driving.
the mot regs in england don't stipulate any distance to take the car to a prebooked mot
The UK MOT regulations used to allow driving to an MOT station - however it's no longer possible to find that in writing (as far as I know!) therefore I wouldn't bank on it (any risk is up to you).
Driving away from an MOT station with a fail is likely to bring risk of prosecution for unsafe car as well as the other problems.
There's many options and laws that can apply and different interpretation's.
SORN is no problem whatsoever. If the previous owner has broken SORN rules, that is not your concern.
After passing MOT the car still can't be driven until it is taxed.
You should be able to tax the car at post office provided you have the green slip (new keeper part) from a valid V5C (4 page document, printed on multicolour A3 folded to A4). You will also need appropriate insurance and the MOT certificate.
An older V5 is no longer valid (double sided A4 document).
UK police have NPR systems in vehicles and at the side of roads - these read the reg automatically and check Tax, MOT and insurance database, with the intention to prosecute drivers who break the rules. I've known people get done when they drove to the Past Office to get a tax disc... I've also known of people getting pulled the same day they got a tax disc (here in Leamington town centre) as the police system was a few hours out of date.
Some of the transport options:
1) The fully legal way is to trailer it to UK (e.g. to get home and then get it up to standard) and also trailer it to and from MOT station.
Ferry company will charge for trailer, and a 2 way journey with trailer only one way may make ferry company ask why. One ferry company tried to charge me a few hundred quid extra as bringing a car to UK for repair was 'commercial' in their eyes and they tried commercial ferry rates on me instead of tourist rates.
[I declined their offer and just upgraded to add £60 trailer cost at the French ferry port]
2) Using an A-frame.
You can use an A-frame for vehicle recovery in UK - however the towed vehicle is then classed as an un-braked trailer and has to be within the allowed weight for your tow vehicle. You would need a trailer board a rear of towed vehicle for lights and reg plate from tow vehicle. It will also need a fog light (trailers more than 4 feet wide need a fog light).
Because this is allowed in UK law, it is allowed across Europe provided you have UK license and tow vehicle (as far as I have found out - EU law allows member state vehicle law to apply in most cases).
Unfortunately in UK, if the towed vehicle is untaxed, you can be prosecuted for 'failure to display' valid road tax. This is fairly unlikely and would need an officious person with good knowledge of the rules who could say that your trailer is actually a working car. If the towed vehicle has no id tags or reg plates and you were unaware of the vehicle ID or foreign registered, prosecution would be harder to pursue, but again don't bank on it. If the car is UK registered, they have a reasonable case for 'failure to display' for an untaxed car towed by an A-frame on UK roads.
3) Register in France.
Seems a lot of effort if you don't intend to keep the car in France, and you would also need to have a legitimate French residence and the time to get the car up to standard, inspected and paperwork done.
4) Drive From France to UK MOT station.
You're untaxed, no MOT and possibly unsafe. Your insurance company would be looking for ways to void you (if possible) in the event of a claim.
5) Trailer in France, drive to UK MOT station.
Same as #4 but should be legal for the French side.
e.g. get a vehicle transport company to deliver it to Ferry terminal.
If the vehicle is without driver, don't expect the Ferry/dock workers to take special care of it - they have been known to drag cars around as quick as they can. I'd be tempted to drive on/off the ferry in person, but only if the car is safe.
Many other options exist and also variations / combinations of options.
For the less scrupulous people, the AA will no longer recover an untaxed vehicle due to people using this as a away to deliver their newly purchased wreck back home!