In brief:
I was towing a car with my van on an A-frame. The car was fully legal, taxed, tested and insured. I have all entitlements on my licence.
A traffic cop spotted me and pulled me over. I got done for no insurance because as I was in control of the towed vehicle, it needed to be insured as if I was driving it. I also got done for faulty brakes on the towed car as there was no way of them being operated.
A-frames are only legal for use to recover a broken down vehicle to a safe place only. And that really does mean, the first safe place. For example: you can use the A-frame to move a vehicle off a motorway but it must be the first junction and no further. You can use it to move a broken down vehicle away from a dangerous corner, but no further.
I went skipping into court with the DVLA Fact Sheet in my hand but got told that it was wrong. I got 6 points and a whopping fine.