Doing a Survey

What's the concensus of opinion out there?

I have regularly used this popular supermarket for my diesel fuel and am the proud owner of a voucher entitling me to 5p off per litre.

A colleague recently told me however, that the cheaper brands of fuel tend to be the 'dregs' from the storeage tanks and therefore may be not too good for the engine.

For the last few weeks I have used only one major brand of fuel but am reluctant to miss out on my 5p saving.

Any offers of advice would be appreciated.