I will have a look in costco myself, there's one in milton keynes 🙂
Hopefully they'll have some - I went to the CostCo in Derby. I'd be interested though as MK is probably closer for me. I think it was 15w40, but they may have other types - even the 5L containers of oil were cheaper than motorfactors/halfrauds.
You need membership, which is £25 afaik (and you need to prove you work in some area, or own a business). And they don't take credit cards - only debit or cash. It's almost like they don't want to sell anything.
Look out for the Aluminium Jack - looks awesome, and I can't find one for sale cheaper (or even the same price) elsewhere.