Where is it actually written that you will not be allowed to drive the car away if it fails ?
From GOV.UK site,
Driving a vehicle that?s failed
You can take your vehicle away if:
your current MOT certificate is still valid
no ?dangerous? problems were listed in the MOT
Otherwise, you?ll need to get it repaired before you can drive.
If you can take your vehicle away, it must still meet the minimum standards of roadworthiness at all times.
You can be fined up to ?2,500, be banned from driving and get 3 penalty points for driving a vehicle that has failed its MOT because of a ?dangerous? problem.
It's only if the vehicle is deemed to have a 'Dangerous' fault that you are ADVISED that it is unsafe to take back on the road. You would do so in full knowledge the vehicle was dangerous & at your own risk !
An MOT tester has always had the option to declare a vehicle as dangerous, the defect would be noted in box C of the VT30/32 & it would be explained to the owner/presenter that the vehicle was not safe to be driven on the road.
Extract from my old testers manual,
Dangerous Defects
If in the opinion of the NT the vehicle has a dangerous defect this must be recorded In box C of the VT30 or In box C of the VT32 as appropriate.
Dangerous defects must be clearly explained to the vehicle presenter.
These defects should be recorded on the appropriate documentation
If that advice was ignored & said vehicle was caught on the road without the defect having been repaired, the driver would be liable to the same prosecution as now, & since around 2005, that info would have been entered onto the MOT data base which is accessible to the police. Nothing has changed in that respect. To my knowledge, an MOT tester has never had authority to impound your vehicle. I certainly didn't in all the years I was a nominated tester.
Regardless of MOT status, it is the drivers responsibility to ensure a vehicle is in a safe & roadworthy condition. Driving one that is not is an offence, whether it was know about or not.
Quite frankly, if you are told your vehicle is a danger to you &/or other road users & you choose to ignore that..... well, need I say more
Regards, Tim