I want to know the answer to the following question:
Which political supporter of Willett's proposal had already used the half-hour version of DST at Sandringham?
All the background I'm provided with is that "The proposal attracted many supporters, including Balfour, Churchill, Lloyd George, MacDonald, Edward VII (who used half-hour DST at Sandringham), the managing director of Harrods, and the manager of the National Bank.". Is that enough to answer the question?