'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.'
I was talking about the improvements to Heathrow. Ferrovial do not own all of BAA. They are however carrying out a lot of the upgrade works at the airport and would certainly be involved in further work to create a third runway and associated tunnels & terminals. This has also allowed them to become a known construction company in the UK.
To say that they would regret buying a large chunk of BAA is incorrect.
They were also a large investor in the crossrail project.