Working off of my experiences of using Birmingham New St, I'd say that ticket barriers aren't that suitable for use on Intercity services, mainly because of large the volume of passengers turning up in a relatively short space of time for any particular train (To say nothing of the volume of trains per hour) and the time that it can take to rectify a gate or ticket fault. :?
Trying to install gates at Birmingham NS would be a very bad idea because of the limited entrance space available, which probabally can't be widened on account of the fact that the station structure also bears the weight of the shopping centre above it. Even if they made the inner concourse a publicly accessible area and put gates on the stairways down to the platforms, there'd still be massive airline-style queues forming as people try and cram through the four gates available per platform!

hock:
When they installed the gates at Waterloo (Which in themselves cause a lot of congestion) they removed a lot of the retail units next to the platforms to make extra space. However I doubt that would be a plausable or even possible option at New St. :?
Personally I think it's about time that ticket gates and I mean ones which are about 5' (1,5m) high (Anti-Vault) were installed in ALL but the smallest of stations to prevent fraudulent travel.
Personally, I disagree. Although I'm perfectly happy with (And support) the current design of gate, the "anti vault" type would cause just as much hassle for legitimate travellers as it does for fare evaders...Aside from the fact that it'd make many booking offices and platforms look like Checkpoint Charlie, or the inmate entrance to a prison! :roll:
Now as it is, I always travel with a valid ticket...Normally a ticket purchased in advance. However I tend to have a foul degree of luck when it comes to time, and even if I aim to be at the station fifteen minutes before departure, circumstances beyond my control do sometimes mean that I arrive there at the same time as my train. In such circumstances where the train is literally just about to depart, being able to vault the gate and get straight onto the train is very convenient for me...And the same applies on the Underground, too.
Does that make me a fare evader?
No it does not...Because I'm already in possession of a valid ticket for the journey being made, and in such instances I normally show my ticket to the guard immediateley after boarding so that (s)he can see that I'm not "Effing" it. 8)
Also, "vault proof" gates are a fallacy in themselves. Such gates are used on the MTA Subway in New York, but when I went there a couple of years ago I had a go at vaulting a few demonstration gates that they'd set up in the subway museum. Not only did I find those gates easy to vault, but their design actually made it
easier for me to do so!

hock: