The problem is that the API uses only the official stations.
This is the google-Maps link for Saffron Walden UK
When I use that city coordinates to get the data
https://api.waqi.info/feed/geo:52.0095521;0.2277959/?token=78312c3771cd11ecb372836690df98c2db1bcc82
I end up in Cambridge Cambridge Gonville Place, United Kingdom Air Pollution: Real-time Air Quality Index
So I have no idea what your nearest “official = validated” Uk station
The full page in the menu can use any station including stations with invalid data.
Steps to follow:
Try to find an official station which also uploads the data to waqi.info
Use google-maps to find the latitude and longitude
Change the lines 325-328 to
$url = 'https://api.waqi.info/feed/geo:'
.'1111111111;22222222'/?token='
.$waqitoken;
where 1111111 should be the latitude and 22222222 should be the longitude
Wim