Right, been playing around tonight. When I updated the software, it overwrote my WLAN configuration again. It did this as I had two WLANs in the /etc/wpa_supplicant/wpa_supplicant.conf file, and it only took the one - the wrong one for my current router!
Having set it all up again, I didn't have to edit the /etc/wpa_supplicant/wpa_supplicant.conf file as the configuration script now does that for you and you enter it as part of the initial configuration. However, I still wanted my static IP address, which the re-install overwrote. I changed my /etc/dhcpcd.conf (/etc_org/dhcpcd.conf) file but it still didn't play ball. I had to go back and edit the /etc/network/interfaces (/etc_org/network/interfaces) file and change
iface wlan0 inet dhcp
to
iface wlan0 inet manual
Phew.