Build a lot of houses as above, finish the motorway network and clear up some of the road bottlenecks, replace Heathrow with something suitable between Birmingham and London, put some proper metro lines in places other than London, speed up HS2, and, in the unlikely event that there is some change from that, build an excess number of nuclear plants and a power line to Germany so we can sell the electricity to them when their ones close.
You just spent trillions. 75billion would get you a few nuclear power plants. Not even enough for us, let alone others.

we need the metro badly up here