Results time.
When we picked up the car it was very full already - a quick plug - I recommend Centauro if you want a car in Spain as when they say the tank is full, they mean full.
After filling up at the start and then filling up just before dropping off the car the figures in between are:
783km travelled.
68.7 litres of Respol's standard Diesel.
Which is 11.3 km / litre or 31.05 MPG (Imp)
Disappointing as it doesn't even match the claimed MPG although I suspect the official figures are for an unladen vehicle as opposed to one carrying 4 adults and 2 ten year old kids plus (far too much) luggage and doing 110-120 km/h on the motorways because of navigation errors and planes to catch.
It didn't have an instant MPG readout I could find on the computer (it was set to Spanish) and I don't have an SG yet so I had to go with techniques I use on my own car but the weight of the van was much higher.
Still it was a comfortable old thing to use and I'm sure with some practice it could do a whole lot better.
Pics attached.
And of course we leave Spain at 30 Dec C and return to Scotland at 15, only to find our new heating system fitted to our house has failed so no heating and no hot water.
I love Scotland...