Heh, after reading in the news about Labour's policy on Capital Gains Tax (a counterintuitive, cross-over generations and across the political spectrum), I fell down a rabbit hole which led me here:
https://ifs.org.uk/election-2024/be-chancellor

You can adjust government spending and fiscal policy to try to reduce the deficit. Don't know how it measures "additional revenue from being a grown-up, sensible country", but it's an interesting challenge.