Re: Horsefeathers -- was it a DDOS or a failed upgrade?
Alister, those 172.16.0.0/12 addresses were not due to the faulty router handing out non-routable, but what happens if BT Wholesale can't reach your ISPs authentication platform (RADIUS etc), or if there's too much load.
Rather than not authenticate you, so your router tries immediately again, they effectively throttle by accepting the login (regardless), issue a 172 address, and you can get to a BT Wholesale page that basically says something like this if you accept the DHCPd addresses and DNS. It disconnects you a bit later so you can try again.
This essentially helps them manage the surge in login demands, but is nothing to do with the original fault.