These aren't exactly uncovered gems and they don't really take much digging, the pension protection is clearly included in the index to the Transport Act and you ought to be able to find the Act on google in about two seconds. Even without reading the Act if you'd attended any of Paul Barron's roadshow briefings when he first announced his intention to do something about pensions a couple of years ago you'd have heard him say that any change to pension benefits would require an Act of Parliament.
That suggests that what they are proposing isn't a change to the protected benefits. If you really want to do some digging you need to find out exactly what the Trust Deed says about benefits. Alternatively you could wait for the meetings because a number of people are going to ask that very question.