I kicked it off overnight and all looked good in the morning. Until, that is, I tried to access the internet.
Everything was ok with the routers and I could connect to multiple networks from other machines but none would work on the newly updated machine.
Searching the internet I found many other reports of a similar issue and most seem to be due to a problem with old VPN software.
This wasn't my situation.
Eventually I found this solution:
Go to: Control Panel > Device Manager > Network Adapters > Select WiFi adapter > Advanced Tab > Roaming Aggressiveness > change to highest.
This worked for me but YMMV.
This worked for me too:
@mrlacey Had this twice I just uninstalled WiFi adapter in Device Manager then "Scan for changes". It reinstalled adapter, all working again— David Hearn (@davidhearn) September 24, 2015