My wife and I have travelled the UK, mainly using C&MC CL sites where we can, and paying as little as £5 per night. It's rare, but at The New House, Fife, we pay typically £20/£25 and also have had to pay for additional electric at £12 for three days.
However, we have just toured France, having only booked our last night through the C&MC at £26.
But, over 1,400 miles in France and 29 days, we paid £7 and £6 on two occasions, with all the other nights being free because we were using aires, three of which had free electricity.
And the beauty is every town in France,
