Especially on a busy train.

Of course, I should point out it is your responsibility to find the guard and pay for your fare, according to railway by-laws. However the chances of finding the guard on a packed commuter/rugby train out of Leeds in the 4 minutes it takes to get to Burley Park are somewhat remote, especially if you get on at the front of the train.

Do they have permit to travel machines on that line?

No. I've never seen them on any lines around here. Morley, my local station, is unstaffed and you just get on the train and wait for the guard.

you can buy tickets in morley now from staff on a morning during the rush hour. Batley has nothing though. Used to have to jump off at Cottingley when I worked near the Arlington. never paid once then as it was packed on a morning and packed on a night