Thanks folks – I went back to my contact at the dealer – and he admitted it was not his speciality – So on Monday he will meet with their motability specialist for advice – and if necessary contact DVLA for guidance.
I am 99.999% we simply hand him the exemption in advance and he will apply – simples!
It will cause him a self-inflicted headache to re-do the finances though since presently the deal includes car tax, despite my mentioning the exemption before we placed the order. At least it’s moving now.
Cheers