Trafficking for sex is covered by the following laws:
Modern Slavery Act 2015
External Link/Members OnlySexual Offences Act 2003
External Link/Members OnlyI've read through the relevant sections and it looks to me like the legal definition of human trafficking for sex hinges on the use of force or the commiting of sexual exploitation crimes under the Sexual Offences Act 2003.
Some key points to consider are that for a crime to have taken place, someone (eg a pimp) has to have forced, caused or incited a person into prostitution or controlled the activities of that person to facilitate personal gain.
So while it is true that
consent to travel is irrelevant to the definition of human trafficking, there has to be someone else controlling, directing or inciting the person for it to be a crime under the Sexual Offences Act and therefore to count as trafficking for sexual exploitation.
So, an SP has not been trafficked if they came to the UK legally through free movement within the EU or by getting a work, study or tourist visa.
They have not been trafficked if they arrange their own illegal entry to the UK and then freely chose to engage in prostitution. Another person can be involved as long as they do not incite, control or force the person.
They have not been trafficked if they freely arrange to travel around the UK to provide sexual services, again as long as they are not being coerced.
I would look at the situation in the same way as any other employment. People may enter the UK from another country to do a job, they may travel around the UK as part of that job and the employer may manage some aspects of that work BUT they have freely chosen to do that work and are free to stop and resign at any point.
I've seen a lot of SPs from other countries who sometimes work in other cities on some kind of rotation. They often leave to visit their home countries for a few weeks and then return. They are women apparently fully in charge of their own decisions, they chose what they will or won't do and who they will or won't see. They are confident, relaxed and in control. It is regularly apparent how much they enjoy the work they do, I am often welcomed with genuine smiles and affection and SPs take an active role in sex, often leading and getting genuine sexual enjoyment from what is happening. I am firmly convinced that this kind of mutual enjoyment is impossible to fake. No amount of pretence can mask someone who is not enjoying what they're doing or has been forced to do it.
I would advise, rather than obsessing over whether someone went to another town to work for a few weeks or spends their whole time touring the country, pay attention to whether the person is happy to be with you and enjoys themself. If they are reluctant, look miserable, seem detached from what is going on or are clearly faking enjoyment then you have reason to be concerned.