The best small SUV for real-world MPG is the Toyota Yaris Cross hybrid, which will easily return upwards of 60mpg. If you want a pure petrol model though, check out the 1.0-litre TSI engine in the Skoda Kamiq or the 1.2-litre Puretech 130 in the Peugeot 2008/Vauxhall Mokka. These are all capable of up to 50mpg, or more if you're gentle on a long run.