End of nothing. Each case is different. I believe this is exactly the advice they give if in close proximity to a police station to sort out such arguments. Refusing to pay for a service is theft, just like stealing. If in a black cab it is perfect because the doors can be locked and the driver has a protective screen. In a private hire vehicle probably not a great solution.
Personally I'd say kick the shit out of them, rub their faces in the spew then if they had any cash on them take it and leave them on the kerb.
You can't imprison someone in a taxi. Yes end of. That's literally what the law says. Your other suggested courses of action are also illegal.
The police shouldn't be asking taxi drivers to bring volatile drunks to the station for them. And if a taxi driver came go harm as a result of that the police would be in deep shit.