It would need to be at least 300 motorway miles. I'm down south and I have family in Scotland plus I do long trips to play in competitions. I know lots of cars have quoted ranges of 250-300 miles but that plummets once you are out of town and driving at speed.
I had travelled to the course using the dual carriageways A27 and A23 so had been tramping along at "motorway speeds".
Got to be honest, I was a bit concerned. I had used a theoretical 118 miles of range to travel 78 miles..... was I going to get home okay with 78 miles left to run with only 92 miles showing as available.
I made the decision to drive the slower route home, and keep my speeds down to around 50mph, no unnecessary overtaking or acceleration etc. Got home with 30 miles still showing!!
Work that one out