[audi4t]

In the UK, fuel consumption is rated at 4.0 or 4.1 l/100km

LEXUS - Lexus CT 200h technical data - A Full Hybrid Luxury Compact Hatchback Car

Why the big difference?

Pulled this off your link



Urban mpg 68.9/4.1 68.9/4.1 68.9/4.1 Extra urban mpg 70.6/4.0 70.6/4.0 70.6/4.0 Combined mpg 68.9 68.9 68.9
The combined mpg converted to US gallons 68.9 / 1.201 = 57.37

I thought the UK would be miles per imperial gallon

imperial gallon = 1.201 US gallons

This is higher than the average US CT mileage usually quoted.

However this may be because US gas is blended with ethanol which has fewer btu's (less energy)