I'm with Sonikk and just about everyone else. i have used the Halfords oil in the past and have never had an issue. Yes it does drop off pressure after a few thousand miles but never to the extent that it will cause damage to the engine as long as levels are kept correct. I've probably done over 20'000 miles on the stuff in the past and its always been good enough that i buy some more. I still run engines in on it now.
I have now swapped to Valvoline VR1 for the rally Mini, but thats because the engine is near on double the power of a standard 1275, that and it has cost me an absolute fortune so i plan on giving it the best stuff i can to keep it in good condition.
It's a bold statement to say that something is 'pretty rubbish stuff', especially when i'm left wondering on what experience that that is based on.