Hmm...
It looks like the running of fibre from LLU exchanges to the door (or at least the green box) will have to be done at the cost of the tax payer. You aren't going to get any of the existing telcos paying for this, especially if they would maybe have to let other telcos use the link. Maybe we are looking at the time to create a nationalised British telecomms infrastructure company to supply this kind of infrastructure to the other telcos. You could call it, err, British Telecom, then sell it off to the tax payer, who already own it for £££s.