I posted this information inn the hope that it may help others searching with the same problem.

My main system is using Xubuntu 16.04 64bit and for the past week or so the panel weather-update applet, ie xfce4-weather-plugin -0.8.6-1 has been unable to show any weather information.

A bug was posted for this yesterday (related to Mint, but same plugin version) to which I subscribed.
https://bugs.launchpad.net/linuxmint/+bug/1692016

Further searches found that it might be worth trying a more recent version of the plugin so I have downloaded the version for Zesty 0.8.9-1 from https://launchpad.net/ubuntu/+source...build/12025316 which installed without problem in Xenial using gdebi and immediately has started working as it should.

I have no idea why the 0.8.6-1 version has stopped, but I do now have a working version; I will keep an eye open on the bug and report back if any other solution is found.