This update could take a while
Having carelessly let my laptop battery go flat, on supplying it with power it rebooted into an elderly Windows 10 on a small chunk of eMMC before I could stop it (laziness on my part as I also need to move the boot partition) and it was desperate to update. I thought I'd just let it get on with it - how long could it possibly take? Seems like that's a question to which I'll never know the answer because after 10 minutes and a total progress of 0% I gave up and caught the boot menu in time to return to the relative sanity of Linux.
However, I suppose it's finally the excuse I need to move that boot partition and wipe the eMMC so it can more usefully be employed.
I'd hung onto Windows 10 "just in case", but the case seems to be diminishing - it gets considerably less use from me than Windows 7 - and casual daily IT is now all Linux and Android. Why anyone would use it for an information display is completely beyond me.