Unfortunately not. If you are building over, you still need to buy the land. And it costs a lot to build long bridges.
If you are building under, you still need to compensate the land owners above, and it costs a lot to build tunnels. A lot, lot more than buying land except when it is residential.
You do however avoid blight payments and dealing with vast numbers of protests and vexatious lawsuits.
How long did the HS2 bill committee spend hearing endless petitions, or discussing them, or the endless route revisions due to complainants of environmental impacts?
Subsoil payments are essentially flat fees and are negligible if the tunnel is buried deep enough that basement developments at future properties are unlikely to be measurably affected.
Buying land takes a long time, whilst tunnels are expensive they involve far fewer significant stakeholders and also cause much less disruption to the surrounding environment, which also reduces compensation and other costs. You don't have to mess around building replacement roads or moving power cables or water mains or telephone line trunks.
The project will cost more but it will actually get built in a reasonable timeframe. You can also proceed in straight lines to your destination.
Given the absurd costs of building anything in the UK these days, adding a couple more billion to put it underground and be done with it is peanuts.
This is why we don't build new electricity transmission lines on shore any more, we bury them in the seabed, to avoid the permitting and public inquiries and the numerous protests.
