waste of £? £12 synthetic oil from eurocarparts/carparts4less will do the same job...
one thing I have learned in life is never cut costs on engine or gearbox oil - buying 4 litres of oil for under £15 may not be the bargain it seems, and £25 over 12 months is about 50pence a week, you can get Castrol Magnatec or similar branded 5W-30 synthetic for that. I know the price of crude oil has dropped recently, but not that much.
I know someone who had his Golf GTi engine rebuilt and then put nasty supermarket special oil in it DOOHHHHH (cost him about £10), engine seized a few days later, may have been his driving style, but who can tell