It's a pain in the arse, but IMHO it's best to stick to the limit and ignore them. When they eventually overtake, which they probably will, stay away from them. As a mate of mine says, just keep out of their danger zone, which basicall means, keep away from them without putting yourself in danger or breaking the law. It's hard not to get the red mist when you see these tw**ts, but best to leave em alone and hope one day the'll get their cummupance. If I see a safe place to pull over and slow down I just let the tw**ts overtake, if not, they can wait. I pay my road tax same as they do.