Most of the thais you'll find in Blackpool, Preston or Southport came here as mail-order brides. Subsequently either the (much older) husbands died, or the marriage broke up due to the cultural and age differences. Once they're divorced they have to work, but cleaning / hotelwork / shagging is all they are qualified for.
The rest are usually younger and are imported, often through family contacts, to work in parlours. Though whether they know what that means is debatable........some come in via dodgy agencies who fund the travel cost upfront and make the girls work as indentured slaves until the loan is paid off. Certainly they're working illegally.........no-one gets a work visa as a whore.