New high watermark for a single journey.
This thing's somewhat optimistic with its mpg guesstimates so I reckon that's somewhere closer to the mid-80s (so about 70mpg US, or 3.3 litres/100km).
Warm weather (about 26C or 80F), and generally keeping to an indicated 60-62mph cruise partly due to traffic (stack of cars sitting nose to tail in the passing lane for most of the trip, so I just ducked out now and then to pass a lorry). 30mins of nose to tail traffic around an hour from the end of the trip which reduced the average speed and the mpg estimate a bit (it was sitting at 93mpg for a while).
Still on 3PMS-rated winter tyres too (it's such a low-performance car I'd rather have it be suitable for the UK's generally quite cold and wet weather and put up with them not being ideal in summer or higher rolling resistance) so could say it's got one hand tied behind its back.
Impressive it's capable of numbers like that but plan is still to sell it soon, as I'm still finding it just a bit too compromised for my use, and I really feel like treating myself with something quicker and more comfortable next...