I think I understand now. NAT loopback was a term I wasn't familiar with until recently but it looks like a lot of people are referring to it as that...
I'm not running dd-wrt on most of my routers anymore, after just about every build for the last year turned out bugged unstable or just outright broken. However I believe what you're seeing is "normal" behaviour for dd-wrt possibly as a result of its firewall or other default configuration. It can be worked around either using custom iptables or dns, or perhaps fiddling with the routing. Easiest option would be to set a manual DNS entry on the router pointing
www.myhome.co.uk at 192.168.1.111 instead of its external IP.