I have tended to find that for 999 calls where there is an immediate risk of harm IE fights, actual violence, unstable individuals at risk of self harm or being aggressive etc the local force will come out to help, sometimes surprisingly quickly. I once intervened where one of the local ferals was threatening to kill a contract gateline assistant who had had his ticket barrier smashed and was unwise enough to get caught with this scummer between him and his refuge.
I initially jumped in, followed shortly afterwards by my driver when he heard the commotion, and between us we herded said lad into the front cab of the train and called 999. The operator said she would have someone there immediately and as it happens within 5 minutes a large group of football fans had thrown the bloke out of the train where he was attempted to kick the cab door down (against my size 11 boot, wasn't going to happen) just in time for 2 of Cheshire's finest to flatten him. BTP appeared about 15 minutes later and took over.
Naturally, of course, known to police, list of convictions as long as your arm, just another one to wallpaper his taxpayer funded accommodation with.
What doesn't help is traincrew screwing trains down in stupid places demanding assistance to remove uncooperative fare evaders. Much better in these modern times to film them on a body cam if you're so inclined and then if they're at it regularly they'll eventually have it catch up with them if it's continually reported - patterns of behaviour build up and an organised sting can occur and mop up any other problems they happen to come across in the mean time.
For us, I know where our BTP stations are and for large chunks of the network you're very much on your own, though again the local forces know that and will turn out if need be - Skegness is a good example where the local bobbies get sent out several times a week to deal with undesirables at the station, as well as things like people who've absconded from nursing homes who head there because of where it is.