I assume the government has some sort of compensation scheme set up so if a project is stopped in its tracks someone pays the wages?

I don't think so. Not sure about the arrangements for a road builder like McAlpine and whether their contract entitles them to contingency payments from their client, but in a case like Tarmac where they might have been prevented from collecting millions of quids worth of gravel its a case of tough, its a commercial risk they have to bear. Amd why not? Permission to develop is a very valuable free gift from society and if society chooses to change its mind so be it.