Hi
As mentioned above, 5w-40 is the most common 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/CFS NT+, Motul Sport/300V, Red Line and Gulf Competition. The Motul 8100 X-Cess, Millers XF Longlife, Castrol...