I know that McMaster does not sell to the UK, but I think these linings are Green Gripper Woven (GGW) made by Scanpac. They have a high coefficient of friction at .52 cold. This is much higher than AM4 at .44. However, when hot the friction goes down to .43, still very good when compared to AM4 as AM4 drops when hot also. I think the static friction is very high at .56. This is good at stoplights on hills.
The cold friction performance is very good because the lining contains aluminum oxide, which is the material in your grinding wheels. Some complain about the higher wear, but I don't think I would be one of them. Several Vincent owners have used these linings for years and like them. I know that Carleton Palmer just put these linings on his Godet front brake. This is not a racing lining, just street.
I would see if your local brakeman can install Green Gripper. It cost me $35/shoe.
David