It certainly states, in the Highway Code, that you should "assist" an overtaking car, presumbly by allowing space to pull back in, or not hoofing it, closing the gap , swerving out into them etc etc, (all things I've had done to me)
Which brings me to the hypothetical situation wherein you are driving your Supra to the edge of town, doing 30mph in the 30 mph limit, the NSL signs are ahead, there is a "Saxo type car" (the point being, its small, and presumably undrpowered in comparison) on your bootlid weaving about. Simultaneously as you accelerate away past the NSL signs, the "saxo type car" goes for the overtake.
Based on the sentence in the HC, should you, by law, back off and let him pass or keep accelerating and let him hang out there until he either backs off, does something stupid or causes a crash?
I can't help thinking that against all common sense, or sense of pride, one should back off and let him pass to be fully compliant with the HC.
For extra value, imagine there is a third car, an unmarked Traffic cop, following you both.