This morning I drove into Chelmsford and dropped into Marriage's Mills for some flour. I bought 3 16kg bags, one each of Chelmer White, Malted Brown and Organic Wholemeal.
The wholemeal has a best before date of May, the other two September. Jan and I get through about three 400g loaves per week (usually I use more like 420g per loaf. I don't weigh very accurately but I always slightly exceed the recipe's weight). Given that 4 loaves use 1.6kg, that means that there would be 40 loaves per bag, or 120 loaves (40 weeks) for the lot.
I use 100g white, 200g wholemeal and 100g malted brown as my default combination, so, given that best-before dates are going to err quite markedly on the safe side, I should be OK.
Up to now, I have shared the flour with Dez & Alex, but they have moved to Mansfield so it's not quite so easy for them just to walk round for a top-up.