But surely you can see that, following a No Deal Brexit, it will not be back to Business as Usual any time soon?
There's going to be an insane amount of work to do. Britain has to work out some sort of deal - or a succession of smaller deals - with the EU to manage the separation of the million and one things that are currently integrated (e.g. air travel, intelligence, medicines, fishing etc. etc.). Britain has to work out what it's going to do at the borders - both with Ireland and at ports & airports. Britain has to put some sort of trade deals in place with someone - and there's some pretty big, pretty controversial decisions to be made there. Scotland is going to want a second referendum, so that needs to be managed......
Investing in infrastructure? Come back in a decade, when we've finally sorted everything out and know where we stand in the world again.
You can only have business as usual if you don't initiate a gigantic and fundamental change in the country's relationship with the world.