Link please. Which authorities? Do you mean county councils interpretation of immigration law, or are you talking about an act of parliament that drives police forces in England and Wales? Or just what you read in the Daily Mail?
And for the ones (for their own reasons) who call themselves 'massage expert', is that also not good enough for 'the authorities'? What about ones who call themselves 'cockle pickers'?
No, I mean UK law as interpreted by the UK Immigration Enforcement teams who are part of the Home Office and have significant leeway in their decisions. They regularly kick girls out who they find working as escorts / prostitutes. There were around 20 thrown out of Lancashire a few weeks back. In many cases they get stopped at the airport on their way in if the enforcement teams suspect they're here to be prossies. And its not a case of what the girls call themselves: its a case of what they actually do, or the authorities think they do.
As for cockle pickers - if legal then they'd be here as agricultural workers -a valid occupation, but the Chinese ones who died were here totally illegally: they'd been smuggled in by snakeheads