MPG for Disco series 2 auto

I'm talking about a D2 td5, petrol V8s must be different. Mind you, once locked up, if on Cruise, you can slow a little and it will stay locked up, but not below 50mph. I know this cos I drive a lot in France where 50 is the new speed limit on all roads other than M-ways and dual carriage-ways. So cars run less economically and therefore less green, Macron you prikc!! Dreadful trying to use top gear in an auto.