So here's a bit of useless information for you all.
Because, during this trip, our fridge decided not to work on mains electricity and due to the weather being very warm, we have decided to run our on-board fridge on gas. We have not used gas for anything else on this trip and all our cooking is by electricity. With the fridge on gas mark medium and using a Camping Gaz 907 (6lbs) bottle, it has lasted us 11 days. Using French exchange bottle prices, that's a little less than £2 per day (ouch ).
Randa