I meant to add earlier that Network Rail are, to the best of my knowledge, looking for signallers at the moment. The role is structured by Grades, numbered 1-9, with 9 being the highest (though these days most boxes are at least a 3 or 4 it seems). It is possible to go in as a Grade 7 or higher off the street if you have the aptitude and life experience. The smaller boxes will get gradually closed and replaced as signalling upgrades are put through, though I reckon there will be semaphores and levers for the next 20 years in some places.
Flying it isn't I'm afraid but it is the sort of job a redundant pilot could apply for off the street and get if they were considering a long-term/permanent move away from aviation, it might be a nice top-up to a pension in the case of early retirement. Training salary is/was only one grade below the grade you'd be in post-qualification, I believe this salary lasts for a year or until qualified, whichever is longer.
The commuter and freight sectors will still be strong I think, there won't be much parking in the big cities and the freight will still need to be moved around. The intercity sector is a bit different because these trains can become commuter trains for part of their journey. For example a 6am out of Euston for Liverpool will pick up a load of Liverpool bound commuters at Crewe at about 7:40-ish. Lots of season ticket holders commute into London from a long way out and even with video conferencing they'll still need to get in. Sadiq Khan wasn't very popular when he cut the tube services and whilst the Train Operating Companies is privatised, almost everything the operators do (including timetable/service changes) has to go through the DfT.