Many thanks to Gardouth (our Web Developer) for working for the best part of yesterday and last night to fix this.
Unfortunately, the CNCC's server (which is based in a UK data centre and also hosted a lot of other websites) suffered a hardware failure. The website is being migrated to a new server, which should even run slightly faster in the long run.
Although the main webpages are back up and running, we are aware that PDF downloads are still not working, and we will be trying to sort this out today so that everyone can access our cave descriptions and topos in time for the weekend.