What about HS1, which runs between stations in London (St P and Stratford) and it's commuter belt?The only new line (not extending an existing line) since 1980 is the Elizabeth line, a significant percentage of which was funded by local taxes.
If you're discounting the various DLR branches since the 1980s then when was the last time the North got a new railway? Borders, Robin Hood Line, Selby Diversion, Ashington were all former railways/freight lines/extensions for instance.
Discounting Croydon Tramlink means tram systems in the north don't count either.
Any one of the following (all opened since the mid 1980s) would put the developments in any Northern/Midlands city region to shame:-
Thameslink Core
Elizabeth Line
The entire DLR
Jubilee Line Extension
HS1 (SouthEastern High Speed services)
Even the Northern Line Extension cost twice what the entirity of Phase 2 of Nottingham's NET cost.
It's the investment we all see, often frequently reported on the national news, subject to TV documentaries (e.g. the £15billion railway), and yes benefit from when we visit the capital. Yet locally often have to put up with nothing more than infrequent bus services that have been run down over the same period and don't even operate in the evening.
It's pretty damn easy to see how resentment arises.
Investment at the Northern Line Extension scale of the spectrum in any of cities would be pretty damn transformative, and even at the Cable Car level of investment would make a noticeable impact.