The grouse are primarily bred to be shot. The fact that they can be sold to restaurants is a secondary consideration for grouse moor owners. So if there is a scarce year, they will shoot less birds in order to preserve stocks, regardless of the demands of restaurants. Unlike most other game, demand for grouse exceeds supply (hence your £40 bill!), although prices certainly drop as the season progresses. I would echo the "keep on eating" advice. The grouse will always be shot in responsible numbers, so enjoy Britain's most delicious truly wild food while you still can - the season ends on 10th December. I have never been. But someone told me you are meant to tip the man who carves your meat at this restaurant, as well as the waiters. Apparently, those who do get a far better cut than non-tippers!