m.tehforum.co.uk is the very same as
www.tehforum.co.uk. Same Beehive installation and same database, just an Apache alias with some mod rewrite trickery to forcefully load light mode.
If one is working and the other isn't then I'd have thought it must be a network issue between yourself and here or something like a stale cache or something else like over zealous anti-virus / filtering.