It wasn't a Tory 3-day week per se, it was a government bodge to fix another bad government idea, namely state management of the coal and electricity pay/supply. With public sector workers being paid too much tax money, to produce too little product, the writing was on the wall. Heath could see it, and did his little best. His primacy didn't last, Labour dragged on the socialist policy for a little while longer until, predictably, it collapsed under its own weight cultimating in the winter of discontent. When the government is in a sinking ship like socialism it will chuck anything at the wall to keep it afloat. For Heath it was a 3 day week, for Wilson it was more tax money. It's an old story. Eventually the answer was to abandon the ship altogether.