Absolutely zero from what I have heard. Apart from Eurostar, XC drivers are the highest paid in the country and therefore management don't feel the need to train drivers up as they'll always get a flood of applicants from other tocs and focs.
The aslef company Council, despite making noises to the contrary, also support the company viewpoint as they are happy for their drivers to basically be paid the premium, funds that could be used to take on trainees.
I'm not sure on The dft position as to whether XC are supposed to take on trainees or not. Perhaps an XC employee on here knows?
There is also the issue of where XC would do the training vs the far flung nature of their depots. I guess the centre of their universe being Birmingham they could train people there but then again, would Plymouth or Edinburgh trainees be accommodated for this time? Expensive.
So as a TM you have a glass ceiling, you can't go anywhere except apply for driving at other local tocs. The effect this has on the motivation and performance of guards is probably unmeasurable, but i would think highly significant. Line of promotion internally should never be seen as a "right" but the morality of not having any line of promotion is equally dubious.