It's an interesting dilemma that you have highlighted - when an ISP suffers routing problems, how can they alert their customers (and what's the point)?
I don't have a solution, obviously. Although it strikes me that a little more redundancy when it comes to Status reporting (eg.. *NOT* hosting the Status page on your own network!) might be a start.
I think however a lot of people probably resort to Twitter and other social networks to find out what's going on, assuming they're accessible, although that just leads to a lot of repetition ("what's going on?" x 100's) so it's not the most efficient solution.
Needless to say a full page apology in the Evening Standard and Metro is the least I expect, and given the speed at which BT fix their major faults they should be able to make the first edition before full service is restored.
What does annoy me even more, though, is that BT claim to have been unaware of this fault for almost 12 hours, when even the most basic monitoring/testing should have identified there was a major routing issue within the network almost as soon as it occurred. Or, equally as bad, BT have known about the problem since it first started and have been working on it for the last 12+ hours, but chose not to proactively inform their customers that there was a major fault, and simply waited for the customers to discover it for themselves.