Have a fairly long trip coming up so wanted to do an oil change before I go. I used to use 10w50 Silkolene Pro S in my Impreza but not sure if it'd be ideal for the Mini.
Its a BMW spec oil (sorry dont know all the figers) there are alot of oils that meet the spec. I use miller oil and have found it good on price and performance.
Try Asda for castrol edge, pretty cheap there & they have got the correct grade (5-30 ?? not sure off the top of my head but that's where I bought mine & reseached the grade before buying it)