This has been done. StarWatch UK was set up in 1995 as an extension to the Japanese and American light pollution monitoring programmes. The programme was launched at the 1995 FAS Cambridge Convention and publicised through both the FAS and Astronomy Now. Many people sent in their observations, but unfortunately, very little data reduction has been able to be done. With the demise of the RGO, there is also now no obvious central address to collate observations.
Discussions are ongoing to try and find some organisation willing to undertake the project.
I now have more information about Gwynedd AS including forthcoming meetings, which is now on the web page. Liverpool AS had people in Cornwall, Austria and Bulgaria. Salford AS were planning a rail trip to Cornwall. This is an ideal opportunity to liaise between societies with the potential of mutual collaboration. And don't forget the best eclipse photograph competition.