This may be quite sad, but have had my 150 PD Cupra for just over a year and have logged all but one fill up, about 16,000 miles. So doing a basic sum on miles covered divided by volume filled, I average 43.9 mgp ranging from 40 to 45 (for a daily commute along the M4 Reading to Slough). The trip computer normally reads 43 to 44 so it doesn't seem to be far out, given the errors involved. It will do over 50 if driven with a bit of care.