again, look at the sticky threads at the top of this section of the site.
I doubt if the section of railway you mention will have dedicated freqs. I'm sure Rich will know more about railway freq usage than I do. The few times I've listened to any railway comms I was soon asleep.
Not sure what system they are on now but on a google search "National Rail ... GSM-R by 2011-13" keeps coming up repeatedly for the Manchester area. Simply means digitally cellular, so longer term digitally encryption. Same GSM-R system here is being installed in all australian metropolitan rail systems & 3-G cellular for the interstate freight network.