Indeed, it's possible. It's probably a mutual thing, and the existing rail-centrism of London would certainly have helped fuel the financialisation of the UK economy. You couldn't build Canary Wharf if no one could get to it.

London always had the better railway lines anyway, privatisation or not. In particular, radial London commuter lines mostly escaped the Beeching cuts. Post-industrial financialisation in London was the crown jewel of the 90s economic strategy. So it feels (feels/reals alert) unlikely that it was specifically the railways being private that led to the boom, but injecting private investment right then could well have been some grease on the wheels.

Of course every private cash injection comes with the long term squeeze as the initial YoY becomes hard to sustain over decades.