Thank you for sourcing it - I was looking for a different type of evidence that stated that it was illegal outright and didn't use the implication that because it would fail it's MOT it was therefore illegal. The bloke I asked did know that car with a spacesaver fitted on the axle would not pass, but neither he nor the other bloke made the connection that you have.
Although I see what you're saying, is it not the case that you are provided with sufficient time to make a car roadworthy (as in MOT passable)? In which case, although illegal, no one would realistically be prosecuted for driving with a spacesaver on a driven axle?
Oh yes they would. VOSA run roadside tests on exhausts, window tint, exhaust NOISE!, etc...and if anyone was running on a spacesaver, and NOT going to a MOT/vehicle repair centre, prebooked, then it's illegal, and they prosecute. They are harsh. I know a member of VOSA from a car forum, and boy are they strict. They would have your car away from you. Running a car, without complaince to the MOT, would invalidate your insurance, and driving without insurance, invalidates your license.
If you had crossply and radial fitted across an axle, never mind odd sized wheels, regardless if you were prebooked into an MOT centre, the vehicle needs to be trailered to the MOT centre.
EMERGENCY RECOVERY ONLY. That means, as I previously stated, that it's illegal to use different sized wheels on the same axle, but if the RAC/AA came out to recover you, and you DIDN'T have a spacesaver, they would charge extra. BUT they are NOT allowed to use the spacesaver, as it's illegal to use on the DRIVEN axle. This rule has been in force since the '60's. (crossply vs radial) even more dangerous using different sized wheels, on a driven axle.
Do you need more proof? Or are you starting to understand what the motoring organisations are saying, and your neighbours are seemingly unaware of? You must give me the name of the MOT tester, that don't know the rules, my CAT convertor has been dodgy recently...