Thanks for the 2 replies.
Just by chance I found that the settings had somehow been corrupted to demand an Administrator to turn Wi-Fi on or off. Odd, as this standard user had previously been able to do this without Admin.
So I changed the settings as in QUOTE below to remove the requirement for Admin involvement and all is now well, just as it used to be.
I cannot explain how the settings got corrupted.
Set advanced Wi-Fi options
You can set advanced Wi-Fi-specific options. For example, you can specify preferred Wi-Fi networks and arrange them in order of preference, and specify whether an administrator password is required to control certain Wi-Fi capabilities, such as turning Wi-Fi on or off.
Choose Apple menu > System Preferences, then click Network.
Open Network preferences for me
Select Wi-Fi in the list on the left.
If Wi-Fi isn’t in the list, make sure you have a Wi-Fi card installed in your computer, then click the Add button at the bottom of the list. Click the Interface pop-up menu, choose Wi-Fi, give the Wi-Fi service a name, then click Create.
Click Advanced, click Wi-Fi, then select the options you want to set up:
Add a network to the network list: Click the Add button at the bottom of the Preferred Networks list, enter a network name, then choose a security type from the pop-up menu. To view available Wi-Fi networks, click Show Networks, then choose a wireless network from the list.
Automatically add networks you joined to the network list: Select “Remember networks this computer has joined.”
Require an administrator password to change options from the Wi-Fi status menu: Select any action under “Require administrator authorization to.”