One Wednesday evening, I was talking to a Scottish chap in a bar in Bangkok. He was on one of his regular visits to see his fiancée while waiting for the British government to approve her visa, a seemingly interminable process. One of her friends came in and we got to chatting and as we all posed for a group photo (selfies aren't new!) she commented on the lump she touched on my shoulder. It's the end of my collarbone, dislodged when I fell 30 metres down an icy mountain and concluding it might as well stay there rather than to pin it (advice: we can but if you bang it again it'll probably pop off and that will make a real mess) I'd got the lump. The bone healed quickly but several months later, the muscles were giving me gip. In less than a minute, applying most of her body weight onto one knuckle, she got rid of the pain. We had dinner and I learned her story: she was from a family in rural Thailand and provided massage (actual massage, nothing hinky) in a hairdresser's in town. All of her income was sent home to support her family. On Friday nights (this is why it was important you know I met her on a Wednesday), she would go to a pick-up bar and look for a European, Australian or American and sell herself: this was how she paid for her home and living expenses in Bangkok.

I thought about her situation: she was under no compulsion, she had no manager or pimp and she wasn't a career sex worker but she still fell within the definition of prostitute.

Back in London, in the mêlée that characterises after work drinks, office and shop girls, primped in workplace toilets, actively scoured the room looking for someone to take them out for dinner and to pay their substantial taxi ride home, everyone knowing that some kind of sexual activity was the price and reward for that, even though no money changed hands.

Over the next three decades, I asked rooms full of people which of the girls was doing something illegal (everyone says the girl in Thailand) and which is the most immoral (usually the answer is the girl in London but occasionally, usually in a mostly female room, the answer is "both."

For the record, I think the girl in Thailand is bordering on the illegal and those in London are the immoral ones.

Last week, I was talking to a friend who was indignant about someone she had met at a business networking event. This woman, in her mid 30s, was in a seven year relationship with a man who had a heart attack and returned to his home country for care intending to return soon. This had caused the woman to think about her position. The man had bought her a car and a home and set her up in a business. He has considerable wealth in his own country which he has said, plainly, is for his children. She told my friend that she was out that night looking for another man. But she also planned to persuade her boyfriend to transfer to her his very expensive apartment and other local assets because "it's been seven years so I'm entitled to it, aren't I?"

The "part time girlfriend" isn't new. Mistresses and "kept women" are as old a concept as the (supposed) oldest profession. And, almost inevitably, the Japanese have an elegant and very long established term for it: Enjo Kosai, a term that inelegantly, via Cantonese, translates as "compensated dating." In Hong Kong, the term fell into disuse after widespread condemnation (and probably overstated) incidence of under-age or barely legal girls being found to be engaging in the practice. What was apparent was that it became a competition amongst some "middle class" high-school girls to see who could get the most, and most expensive, gifts. But to put this in context, it's no different to American school and college girls "dating" a "jock" to get his ring as a trophy. But the Hong Kong situation became news when it was revealed that one "ring" had 100,000 members. With a population of about 7 million, if we scale that up to the population of the USA (about 370 million), the number would be about 5.3 million. The International Union of Sex Workers estimates that the figure in the USA is between one and two million, and that's taking all sex workers into account, not only compensated girlfriends.

In the past 30 or so years, dating for gifts has become more than simply socially acceptable: it's a badge as important as the logos on the handbags that are the basic reward for a job well done. Websites exist for the sole purpose of introducing the well-heeled (or those with borrowing capacity) to the (usually) young and willing in return for gifts or, even, money.

In 2017, syndicated newspaper stories circulated where two "PTGF"s (and one boy) told their stories and other reports around the same time trawled Instagram and other social media sites finding a significant number of adverts. Today, we can find subtle ads all over dating sites: loves "to travel", "eating in good restaurants", "attending concerts", "nice things" are juxtaposed with "caring", "loving", "attentive" and similar terms. One dating site has multiple names attached to the same photo, one of which says "Happy Go Lucky And I Love Travel Too" and nothing else. The phrases "I like nice things" and "I enjoy luxury travel" are key indicators.

But even this isn't a recent fashion – so-called "lonely hearts" columns of newspapers included, for decades, clear indications that a woman would date only financially secure men with their own home. Is this a filter or a hidden hint: don't try if you can't or don't intend to buy?

How does this fit into the left-wing. ultra-feminist, anti-family, narrative that marriage is legalised prostitution? Is the engagement ring a deposit against the future payments that will be made? These arguments have been raise many times over the past 120 or so years and regardless of how offensive many find them have at their heart one essential question, the same question as the law has grappled with for even longer: where does the moral balance lie and is national law the correct place to make those determinations? If not, do we fall back onto the morality of religions (which have long had an ambivalent relationship with sexual morality) or into the attitudes where the family should be undermined because all loyalty should be to the state?

These are not what we might consider career prostitutes. Some offer nothing more than to accompany someone for dinners and social functions for very modest fees and even say what they are saving for; others are somewhat more open about their intentions. Many are literally the girl next door – someone who provides services for money to pay tuition fees, for example. Some are blatant: they want stuff, expensive stuff, the stuff of badge-jockeys where labels matter more than style.

So that begs the question: if payment is in money, that's prostitution. So much is settled, ish. Is it still prostitution if payment is in stuff?

And how much stuff qualifies? Is a quick shag to thank someone for dinner included? A quickie in the Porsche after being driven home after a night in a club? A Lana Marks bag for spending a weekend in a ski lodge? Are Hermès Birkin bags given on a sliding scale relating the price of the bag to the level of services performed? Is price a determining factor? Is value? Is the price negotiated up front? The girl in Bangkok told me that she cannot name a price: she always has to say "it's up to you", a phrase that has found its way into the vocabulary of South East Asia and is far more common than "no money, no honey" which is reserved for later, when it is clear that a relationship is more transactional than emotional, on the part of the woman.

There's one common thread so far: the women are all volunteers who choose their lifestyle even if it is thrust upon them as a result of desperation. But there is a further complication: what if it's not voluntary, or not entirely voluntary.

There is an argument for saying that in every case where the woman (let's keep it simple but note for the sake of completeness that it might be a man) takes part in circumstances where there is an element as a result of which her consent may be negated is rape.

But not all negation of consent is clear cut. For example, is a drunk or drugged woman capable of giving the necessary consent? What if the drink and drugs were entirely self-administered and she targeted a man for sex then claims he "took advantage of her"? What if she uses that claim as the basis for a demand for money, etc. And what if the drink or drugs were administered, or at least facilitated, by a third party? Is there a difference if that third party was a "friend" doing it for a lark or someone controlling her to the intent that she would have sex with someone?

The question of consent in the case of self-administered drink or drugs is outside the scope of this article. And so is the question of someone getting a girl drunk or giving her drugs so he can have sex with her.

But the question of a third party creating intoxication to make a profit from it is exactly what we need to consider for it goes beyond questions of rape and to the heart of prostitution.

To but it baldly, if one person coerces or by other means influences another person to perform sexual services for reward, is the second person guilty of prostitution?

The debate rages in multiple jurisdictions around the world and is complicated by the use of the term human trafficking which is, itself, open to wide interpretation.

It's complicated still further when the woman gives actual but not legal consent: how can a man approached in a bar and taking the woman to his hotel room form suspicion, much less knowledge, that the woman is under duress from a third party? So far as he is concerned, she is a prostitute while campaigners say she is a victim. Can they both be right?

If police officers identify her as a victim, what options are open to them? This is a politically sensitive question. It's not even a conservative v progressive area of dispute. True, there are radicals on both sides ("it's my body, I can do as I like" v "sex should be reserved for the purposes of procreation in the marital bed") but in the world most people inhabit, it's not a question of ideology, but of a general feeling that it's something sordid that they would rather didn't happen. And then, of course, there's the associated criminal conduct including organised crime. In most jurisdictions, there is no option - the woman must be arrested for prostitution, even where the arrest is for her own protection. Laws must be remade to take account of forced or coerced acts that would otherwise be classified as prostitution. But that comes back to politics.

In South East Asia, there is a circuit: a city in China then the capitals or large cities, or large events, in Jakarta, Singapore, Malaysia, Bangkok, Manila, Tokyo, Hong Kong – and increasingly Sydney and Melbourne. Travelling on tourist visas, women (mostly but also men and transgender) spend two weeks in one city and move on. Many join the travelling circus entirely voluntarily, and go on tour two or even three times each year. They are often characterised on dating sites by information that the person is in a particular city for two weeks or so. Those that do not achieve the targets set by their tour promoters and they find themselves in trouble, told to commit obvious crimes to make up their shortfall. Targeting and drugging men during the afternoon and taking them to a hotel is far from uncommon. The lucky ones wake up having been robbed; the unlucky ones don't wake up.

It's obvious, then, that consent at the point of delivery may be a sham but the target has no idea it is a sham. Indeed, he may well be very flattered by the attentions of a woman that would usually be out of his league and he knows it. Even when he tumbles to the fact that he's going to have to pay, he's almost certainly blinded to the risk that she is controlled by someone else.
So the authorities have a problem: on strict definitions, the woman has been raped. Where it is an offence to rent a prostitute, he becomes guilty even if he did not set out to be so.

And the woman? Does prostitution require mens rea and if so does coercion negate that? If so, is she innocent of prostitution in the eyes of the law, even if she is guilty of other offences?

The final question is that of a third party exercising coercion. Some have argued that he (or she, but again let's keep it simple) should be regarded as guilty of conspiracy to commit rape but that argument can survive only with a series of legal fictions and devices.

Far more reliable is the old standby of living off the proceeds of immoral earnings – but only if the definition is updated. Why? Many people consider prostitution to be immoral – while themselves taking part in all the various schemes we started with. And that requires a fundamental rethink: who determines morality and should the state interfere. If the state does not interfere, who has the power to do so? Historically we would have said it is the church but what church, and what about non-members? What about a sect that actively promotes sex with minors or a religion that forgives it if the man marries the girl, even if she is only 12 years old? Can we trust those with such rules to determine morality for all?

There are topics I have not discussed for example, the question of parents charging for online abuse or static photography involving their own children.

Hopefully the topics I have raised will result in thought and discussion. I have deliberately not suggested responses so as not to direct the readers' thinking.