I read with interest a recent article you posted regarding supermarket fuel and thought I would share my feedback. Following your advice, after purchasing my Nissan X-Trail in 2004, I used only Shell or BP and occasionally Esso but never Supermarket. I covered approx 110,000 miles before handing the car to my wife. In all the time the car was serviced, latterly by our local one-man band, there were no issues with fuel system and economy was good. My local garage reported at one service, that he was replacing the filter because I had asked him to, but in fact it was as clean as the day it came out of the box. My wife, not being quite so pernickety as me, sought only the cheapest fuel and also most local both of which meant supermarket.

We had a problem with the car in Autumn 2011, which having been variously diagnosed as EGR, Camshaft sensor, etc., was ultimately tracked as a completely blocked fuel filter. It may have been coincidence, but the valve within the filter housing also had to be changed. Part of the reason that we eventually traced the fault to the filter, was a chance conversation he had with a technician in a major Volkswagen dealer, who was complaining about major issues that Volkswagen were having with fuel filter blockages, which they were blaming on supermarket fuel. My wife is now converted, and uses only brand fuel. I will make sure the filter is changed on time, if not early.