Prophead,
LHR has always been an entangled mess, but on the plus side, T5 was brand new, and that in itself was a £4bn investment.
I think you need to look deeper into it and see exactly why Ferrovial bought BAA. Who do you think is doing these improvements? Who is building a large chunk of Crossrail?
From what I see, there are numerous different contracts for different sections of tunnel, then again for the stations and surface work. Ferrovial are just one of many players here, all the big construction firms seem to be represented, not sure I see a connection between that and LHR.
If FV are willing to sell LHR at a 'reasonable' price - as they will then get major part of construction contract or ownership in the new Thames Airport, then that would be a major step forward. However, for the time being, that is purely hypothetical. I still repeat - even using back of envelope stuff, what is the business case? How many passengers pa would be needed at a PSC of £x, spending an additional £y in terminal and other spin-offs to make it work? Even with BAA/FV on board / out the way, Island Airport is further from the centre of London than Heathrow, meaning LGW becomes potentially just as attractive, and it can easily undercut on PSCs. Sure, attach Thames Island to Crossrail, but that stops virtually everywhere en route, ok, add a link straight into St Pancras, but is there the platform space. Now as said before, these problems are not insurmountable, but they could push the costs up still further. The Foster rail link around the edge of London would also add a few billion, and create a number of additional technical challenges.