Yes the site has been with Google places for ages.
I think I've found the answer - two in fact.
The first answer is that I'm absolutely stupid.
The second answer spins off from the first; I should have realised that as regards mapping Google trusts you if it can find you. It can't find this property because its address (as far as Google is concerned) simply doesn't exist.
Because about four years ago, the local authorities in their infinite wisdom (this is rural Italy remember) decided to change all of the road names in the village - the population of the village is around 200. In their defence there only was one road name for the whole of the village and low and behold if you Google that original road name Google will immediately take you straight to it - and that without any reference whatsoever to the country. Now it's also true that the new road name exists and Google will show you lots of option within Italy but not anywhere remotely near the location of this property.
So there we have it.
What I've just done is to upload a geo sitemap file. What I will do next is to upload a microformat contact details hcard. If that doesn't work I'll consider changing the property address listed back to the old original address which as we know Google Maps can find without difficulty.