From the perspective of someone who's not employed by the railways...
Ultimately, no job is more permanent than the notice period, and as far as UK employment law is concerned, there's very limited protection from unfair dismissal and no entitlement to redundancy pay if you're sacked / made redundant within the first two years of a job (you are protected from day one on equalities law, e.g. race / sex discrimination and the like.)
The question about 'no compulsory redundancies' is a valid one, which someone more directly knowledgeable may be able to answer.
One on hand, the fact they are (if I've read it right) offering you a permanent contract is encouraging - some TOC's seem just to have left vacant ticket office posts unfilled for some time now, and I've seen others advertising on a 12 month fixed term contract basis.
But having said that, even if there's a 'no compulsory redundancies' clause, what are the options with a TOC employer if a particular role at a particular location is redundant - what 'alternative employment' in terms of job role, pay level, shift pattern and location would a TOC have to offer? (again, I hope others may know more than me.) Is there a risk that any 'alternative' they offered might not be acceptable to you?
Is the 'pay protection' referred to one where you stay on existing grade and get inflation pay rises? Or the sort where you stay on the same cash amount until inflation means the pay grade for your new job overtakes it? And is it limited to X amount of time? (I've never personally been on it, but the latter is how it's worked in places I've been at where it has been a thing.)
30+ years is a long time with one organisation - how secure is current job however fed up you are? (or if it's not that secure, is there a chance of redundancy any time soon? 30 years' service would mean a good redundancy pay deal) and what are the respective pension schemes like? are you in a line of work you would be able to go back to (even if not with current employer) if this goes pear shaped? If you've been in current role that long, then you must at least be in your late 40s - from personal experience, some employers / potential employers are not keen on older workers (yes i know age discrimination is illegal, but some employers haven't really taken the race discrimination laws seriously yet and they have been on the books 50 years.)
While I've asked a lot of questions, I'm not expecting you to answer any of it on here, just putting it as questions you might want to ask yourself.
Best of luck, whichever way you decide to go.