You've really got to think laterally here.
BA/IAG buy KLM from loss-making Air France. A new off-shore airport is then built for BA/KLM to share as their home base in the middle of the North Sea, well away from any people at all.
The new Schip-row Airport is built for a modest £1,000bn with 12 runways in all directions and will be completely self-sufficient due to the 10,000 wind turbines located on the rail bridges from London/Amsterdam.
HS3 is then built at £500bn so that both countries can access Heathrow-Baan in only 30 minutes from central London/Amsterdam.