I had a look in Halfords the other day actually, the ones they do for our car (Cupra TDi) are their own brand 5L 5w30 for £42.99 (+ free £20 screwdriver set) the Mobil 1 ESP for £49.99 for 5L and Castrol Edge for £45 for 4L
To be fair, Halfords oil will probably be Castrol made anyway!
As much as we slate Halfords, at least they are relatively helpful, I tried GSF and was simply asking for a price on the oil he had behind him (Fuchs) it was the right one and he kept contesting me, saying it wasn't for my car, looking in books etc, when I knew for a fact it was the right one, but in the end I left, so I won't be using GSF and their friendly services again! (And an Audi dealer trying to sell me the wrong Quantum oil as well!)