They just want to see that you have showed a bit of Interest in them, don't need to give tons of numbers/details. Just say Gtr caters for 30/35% of all passenger journeys in UK. Plus those gn routes and all will be good on that front.
See thats where I am confused lol but if you passed it should be ok but I read go ahead as a whole caters for 35% but gtr on its own is 22% but if you said 35% I shall go with it mate lool