Silkolene Pro S 10W50. It's around £50 per 5 litre can, but you won't get a better oil!
Opie Oils is where you want to get it from. register on their website, give them your club (IMOC) along with your username iirc then you'll get 10% off of everything automatically.
They often do a deal once a month or so where it's £38 for the bottle... unfortunately, one of these deals finished on Tuesday so you're out of luck there I'm afraid!
Definitely the oil you want though! If in doubt, send them an email or give them a call telling them your car, and mods and they'll recommend one for you!
Good luck!
what mileage is on the car??how often does it get used??do you do any track time??is the car left outside or is it garaged,all these questions need to be answered to find the right grade oil for your car
^^^^^ He does have a point!
As I said though, have a chat with the guys at Opie Oils and I'm sure they'll ask those questions and advise you accordingly!
Good luck with it all!