Hi
I would use a 5w-40 synthetic as the best option.
http://www.opieoils.co.uk/c-656-5w-40.aspx
Out of those, the best ones are the Fuchs/Silkolene Pro S, Millers CFS NT/CFS, Motul 300V, Redline and Gulf Competition. The Motul 8100 X-Cess, Millers XFS, Shell Helix, Fuchs Supersyn and Mobil Super 3000 are good, cheaper alternatives.
As a budget choice, a 10w-40 will be fine and I would either go for the Fuchs Syn MC, Shell Helix, Millers Trident/EE Nanodrive, Castrol Magnatec, Mobil Super 2000 or Motul 6100
http://www.opieoils.co.uk/c-657-10w-40.aspx
Cheers
Tim