Ah, you mean the "free air tax". They did finally invent a way of charging for its use, we said they probably would.
However, the OP's question was actually about the altitude that pilots sometimes choose to fly under controlled airspace and why. I had hoped to explain in simple terms why sometimes pilots fly close to the base of it, rather than get drawn into an argument about who knows the UK VFR/IFR rules best.
That's all. I'll leave it there, now thanks.
