I work for one of those businesses and we were affected. The reason we didn't have a backup line, is because the other major ISP (Virgin) doesn't have its fibre in our region. Therefore, BT is our only option.
Edit: you could also consider a backup line from an LLU provider. You still have the copper as a single point of failure, and perhaps power at the exchange, but the infrastructure is different.
Not exactly true, the non-BT option is primarily Virgin. Virgin has a pretty good infrastructure (at home I have 50Mbps broadband from them) and generally they are cheaper. BT on the other hand is more expensive. If available I'm sure businesses would select Virgin. But we (I work for one business that is stuck with BT) have no option but BT because Virgin doesn't have its fibre in our region.
While BT runs over telephone wires. Therefore is more pervasive in the UK.
Mine was out for 4.5 hours yesterday.
They seem to be down playing the outage, the paper this morning mentioned that it was out for only an hour or so.
When I spoke to a support guy yesterday he said that 30% of their network was out and this was 4 hours into the outage.
Using 3G as my local exchange is actually out, sad that so many businesses did not have a backup if they are dependent on a single point of failure for revenue.
It's a shame that these businesses that have so much hinging on their Internet connections don't have any kind of backup line arranged.