Unable to allow/deny access to IPs
Solution 1:
Thanks to @ChrisLam's comment, I realised that the IP address being shown in the access logs wasn't the same as my current IP.
This IP, 108.162.225.167, appeared to be matched with the servers of CloudFlare.com, which we are using to speed up the site.
Although there was a rule set to not cache this page, the IP addresses of requests were still not being passed back to the server. CloudFlare say that:
"Because CloudFlare acts as a proxy, you will notice changes to the way that your website visitors' IP addresses are displayed both in your server logs and web applications - notably that all access appears to be coming from CloudFlare IP addresses."
Installing CloudFlare's mod_cloudflare
module for Apache httpd allows these IP addresses to be passed back to the server, and fixed my problem perfectly.
Download and information available on CloudFlare's site: https://www.cloudflare.com/resources-downloads#mod_cloudflare