Here's what I recorded on my 'normal' 3 & 3/4 hour, 220 mile 'commute' from Central London to Liverpool this afternoon. 'Consump. 1' and 'Avg. speed' were reset when I left the petrol station in London, and the photo was taken as I parked the car at home in Liverpool. The average includes (of course) the motorway cruising and the 20mph driving around London! Didn't go above 20mpg until I'd hit the M4 as there were too many stop-starts at traffic lights & such.
It was showing 31.3mpg until about 20 miles from home, but I floored it a bit to overtake some dawdler in a 307 turbo-diesel doing 40mph in a single lane NSL - who then accelerated up to 60mph and attempted to tailgate me, obviously for having the audacity to overtake them - so I floored it a bit more and they disappeared

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I'd also assume it'd be better if I had reset it once I was out of suburban traffic, and if I could have avoided any jams.