I used to run a standard plug & now notice how clean the iridium one is compared. I'm with coastie on getting the highest octane unleaded you can. In Australia, BP make "Ultimate" which is 98 octane. Dont quote me, but Caltex make "Vortex" & I think it also has 98 octane rating. Normal premium unleaded is only 95 with standard unleaded being 93.
Is the same in England ?