Not sure that’s true. One of the first things Boris did after Brexit was start pushing hard on infrastructure spending with projects like HS2 (already on the books, but Boris explicitly threw his weight behind it, and got rid of objectors) and “levelling up” the north.
Think Boris realised that all those labour voters that voted for him wouldn’t hang around unless he substantially improved the quality of life outside of London. Big infrastructure projects are the obvious path to take.
Boris also increased business rates as well, along with being caught saying “fuck business”. Boris isn’t your standard conservative, looking for economic stability or growth. He’s only interested in what keeps him in Number 10. And big spending up North looked like a pretty good strategy. Who cares about ROI for the tax payer, when it’s gonna keep him in office?
Personally think the spending is/was a good thing on the whole. But I really don’t like Boris, and his complete lack of any conviction, except his conviction of reminding in Number 10.