Disabling Fast Startup in Windows 10

A strange bug seemed to have crept into a Win 10 lappy: Live mail would only start once a day, and Chrome would sometimes not start at all. And shutting it down was very slow - like several minutes. As an additional oddity, the Group Policy service was not being started. On a different lappy, these were fine, but shutdown was taking several hours!

Finally, sussed it as being a problem with "fast startup" which seems to conflict with some apps: Chrome and Live mail particularly. It seems it's to do with "fast startup" not being a "real" startup like "restart" is, but a halfway hibernate which means that problems don't get cleared properly.

But... it's not exactly obvious how to turn it off, either ... and it defaults to on.