You're not kidding! think I'll just give up on the subject, and try and get the info elsewhere.
In all seriousness mate, too many variables... not many people have owned both, some have heavy right feet, some dont... Some see more motorway than country lanes, some dont leave towns!
And the difference as noted will be very little, lots of people take very little notice...
3FIDDYZ is spot on.
Even in a "scientific" test you would have to have the following criteria.
1. 2 cars. One JDM, one UK.
2. Both would have to be 100% stock, built in the same year, running the same fuel from the same garage. Need same tyres and the drivers would need to be same weight.
3. Both cars would need to be at EXACTLY the same speed on the same roads at the same time.
4. Both drivers would need to have identical driving styles.
I'm sure a "result" of any kind would demonstrate a minute difference in MPG.
For what it's worth, I run a 2003 JDM tiptronic on stock tyres with a JDM pop-charger and K1 exhaust and get 7.7 km/l. (21.2 mpg)
But then I do short trips and drive like