The bbc are a bit behind, but have been talking about doing the same for a while now - and appear to be building this archive of (currently just very old) programmes out gradually:
http://www.bbc.co.uk/archive/
Not sure whether it can be accessed from ip addresses outside the UK though...
I've been waiting with baited breath for the BBC to offer it's content on the web internationally too. (They are in talks with google about this supposedly). It's a MAJOR bummer that we can't access Channel 4 or the BBC on the web here in the states. It's actually really really frustrating.
It's funny it doesn't mention UK in the title. When I first read it I was a little confused. Here in the US channel 4 could be completely different even 10 miles apart.
Buggers.