Thank you gentlemen (or ladies?)
F S D - I had a quick look at the Tom-Tom in PC Worry and it seemed to be less favoured than the Kane, but that could well have been the 'commission' effect. However your experience seems to put it in the frame, at least.
WCollins - I take your point entirely - especially since this PM I saw the Kenwood in action

That really is the canine's cojones. The problem is:-
1. that it has almost spoiled me for anything else and
2. that at £3k (but it does include fitting!!

), I have something of F S D's pocket and arm length juxtaposition!!
I shall have to keep looking and maybe stick with paper maps for a while longer