I'm certain that reopening old lines will be cheaper and have more benefits then a new express line. The HS2 reports are all based on information that was disproved. HS2 will actually leave some places, like Leicester, worse off economically. I doubt reopening local lines around the country would cause such problems. And the speed benefits are based on old data where the MML is concerned. It also won't reduce CO2 emissions but stay neutral. The jobs created are very costly per job and likely include relocations. The cost of using HS2 will be higher than current services which will be reduced in some way on ECML, WCML & MML as another thread discussed. The stations are not well placed on the east section. It misses the benefit of allowing overnight freight. It's likely just to extend London commuter belt to the detriment of the rest of the UK.
More places should get new lines, rather than already connected places, where there's still options for other improvements on existing lines. We don't need trains to go faster as the distances are small in the UK unlike France.