I recently did a work trip from Derby to Brighton and back.
Driving down doing a steady 70mph all the way (I was in no rush and had my boss in the car with me), I averaged 42mpg. I then spent 15-20 minutes driving through brighton at rush hour, it dropped to 41mpg.
THen had a drive to Littlehampton on the coastal road, still kept above 41mpg.
Driving back up North, the MPG dropped below 40 (39.7) until I reached the M25, then at 70mph again it climbed to 41.5mpg when I got back to Derby. At this point I had done 410 miles, red light was on but computer was showing 65 miles until empty. I filled up at the same station I had used the day before. MPG calculated from receipt was 41.7mpg, so only 0.2 more than the trip computer.
I was very pleased with this. And on that basis @ 1.359 pence per litre (at the time) £35 could have got me 236 miles.
Normal driving however is not this good, my average is 35-36mpg depending on Derby traffic.
Still great for the car, but unfortunately as I will soon be doing 330 miles a week by beloved coupe will probably be replaced with an eco wagon.