While I’ve found the Motability car search a tiny bit helpful in getting the correct AP I have to use other ways and means to get the correct information about cars and by this I mean seat, boot, door, seal heigh measurements etc. and where these are available there often incorrect or out of date and knowing how many litres a boot holds is as useful as a chocolate tea teapot.
Best bet is to look at the cars you think are suitable for you (i.e. getting a short list) then make a trip to a showrooms with tape measure in hand but as far as MPG goes, forget it even though were told the new method is more accurate but I do wonder.