Quite feasible yes
BT IPStream I think is about 1000 customers for a 34Mbps Home Gateway
Based on there being 1269 BE / O2 unbundled exchanges in May 2011 (not many gone live in the last 6 months
625000 / 1269 = 492.51279 as an average number of customers per exchange
Rounded up to 493 average no. of BE / O2 customers per exchange
For 28 exchanges that makes 13804 BE / O2 customers
1Gbps should be adequate then for 13804 customers and I wouldn't be surprised if was more than 1 circuit or 10Gbps these days
It should certainly have been enough in Feb 2008
Be* Unlimited