That's exactly the journey I made with the MKI Prius - with a full load of passengers and luggage. It simply couldn't keep up on motorways - the M6 especially was a bad joke for a 20 grand car. And the fuel consumption was dreadful due to being thrashed hard to go at normal motorway speeds. It did almost exactly 10 mpg less than my then petrol BMW 525 auto over that journey. The passengers also hated it - poor ride when laden. Wallowed all over the place. It was better coming back solo - but by then I'd learned to hate it. There is no point in having a family sized car at that sort of price which is so outclassed to drive anywhere other than in town. Of course Toyata specialise in this sort of thing. The vast 4x4 Lexus
400H can't do any of the things a proper 4x4 of the same size can either.