Well a bit of an update........the 180 is running fine....thank goodness!
Filled it up today having reset the mileometer at the last fill up and with the cost of the fuel (LPG) and distance travelled it works out to be the equivalent of 50.84mpg!!!!
Given that most of its running is on a daily 50 mile slog across rural Norfolk with lots of accelerating and braking I'm pretty pleased with it, in fact it's working out cheaper to run then the ZR TD it replaced, just as long as I ignore the occasional £1000 repair bill