I came across a website for tracking fuel economy and comparing it with similar vehicles: http://www.fuelly.com
It's fairly simple and just does what it says on the tin. It has a bit of an american bias, but you can get it into UK units (UK gallons + pounds) by clicking on "UK" in the top left corner. You can also enter fill-ups via your smartphone (iPhone or Android).
Not that I expect many 260 owners will be keen on tracking fuel consumption, but it would be interesting to see a comparison!
At the moment, it doesn't have ZT listed as an MG model, so you have to follow these instructions:
http://www.fuelly.com/faq/8/vehicle-is-not-listed
And you can use banners like this: