Sex work – at least, heterosexual sex work - was not illegal in England: that is, it was legal to exchange sexual services for money.
However, there were various laws relating to nuisance and disorderly conduct and vagrancy which might be put into play to police open manifestations of prostitution. But there was no licensing system such as existed in many places in Continental Europe, with a police register, designated red light districts, medical inspections, etc.
It was possible, if not entirely common, for a young woman like Clorinda, of humble and obscure origins but gifted with beauty and intelligence, to deploy her charms to become the richly-rewarded companion of elite men, a leader of fashion and a maker of taste, and she might even make an aristocratic marriage, or at least obtain generous settlements. However, there were considerable pitfalls, and the career of Emma Lyon, later Hart, subsequently Lady Hamilton, illustrates several of them. If a woman in such a position bore a child, it was very likely that she would be obliged to foster it away in order to continue her career, as happened to Lyon, and was also the case with her later child by Lord Nelson.
At a somewhat less exalted level, there were the ladies who pursued their trade in and around Covent Garden. This was such a notorious area for sexual licence that over a significant period of the later eighteenth century a guide, Harris’s List of Covent Garden Ladies, was published (several editions are available online and linked at that article).
There was also a good deal of street prostitution, as well as more casual prostitution. I have seen it alleged that women who were ‘really’ prostitutes would give their occupation as, for example, ‘seamstress’, on the census or if taken up by the police. The fact of the matter is much more likely to have been that they were employed in the notably precarious and seasonal needlework trades and occasionally obliged to supplement their meagre earnings with sex work. They would not, however, have considered this their occupation or identified as prostitutes. There was also an intersection between prostitution and petty crime, with, for example, women soliciting men with the expectation of sex in order to get them alone to rob them, or have a confederate rob them.
L.A. Hall, FRHistS