A saga of bed linen in an unspecified number of sizzling parts…
Well, I did my research, as flat-earthers and anti-vaxxers are wont to say, and I came up with just one fabric supplier who does polycotton anywhere near wide enough for a king size duvet cover. And I ordered some in a fetching mint colour. Even so it’s still not wide enough to do it in one go: it’ll have to have a seam set rakishly to one side. But it’ll be good to do some sewing again. It is very satisfying to make something exactly the way you want it, as opposed to choosing from what’s in the shops, and if I’m lucky there may even be enough left over to make a matching pillow case. Sweet.
I’ll keep you posted on my progress.
Kirk out
Sarada Gray 
Glad to hear you found what you needed. Good luck with the sewing. I’m surpised John Lewis didn’t have what you needed. Their store in London has a huge material section, and they deliver online purchases.
Best wishes, Pete.
Good point, I’m sure they would but I thought they would be out of my price range
Understood.