From memory, in the past the Motability insurance covered us to drive a dealer supplied courtesy car when the Motability car was in for a service, but they don’t even cover that now. I recall some years ago a dealer telling me that this had been withdrawn and I had to take out their insurance. Dealer provided insurance can be sobering. I’ve had a number of multi-day test drives recently and the excess was £2,500 which was a bit disconcerting when I was testing a high performance car and wanted to drive it in anger
That cover is still in place, the dealers just prefer you to pay for their own insurance. The insurance certificate specifically mentions being covered for test drives to assist suitability and temporary replacements for servicing, etc.