During the one super-freezing weekend we had in February where the temperature reached -10C my Mazda6 Sport (09, diesel 2.0) consistently cut-out and wouldn't go above 2000rpm or 40mph.

I spoke to my local Mazda dealership who said a number have had similar issues that weekend - and put the problem down to the diesel quality and turning 'waxy' in the freezing conditions. I always use Shell regular diesel and understood this was one of the better fuels to use. Is this true or is there anything else to consider causing this problem?

The following Monday when temperatures were back to normal the car behaved as normal with no problems and I've had none since.