In the olden days – before the launch of the iPhone, in other words – people who couldn't find love by asking out someone in a bar, a club or at work (yip, folk really used to do that) often relied on what was known as “the classifieds”, short adverts in newspapers and magazines littered with coded dating terms such as GSOH, WTLM and GCH. Actually forget that last one. It stands for gas central heating, thought a cosy flat could have its appeal for a prospective suitor.

In these adverts you'd find any number of Romeos in need of Juliets, Darcys in search of Elizabeths, Darcys in search of other Darcys and maybe even a Spock or two in search of a Lieutenant Uhuru or Nurse Chapel. Or both. In the field of human sexuality, you see, pretty much anything goes and you could find most of it in the classifieds.

In fact, you could find most of it in the London Review of Books, whose classified section was (and still is) legendary. This one is fairly typical: “If intense, post-fight sex scares you, I'm not the woman for you (amateur big-boned cage wrestler, 62)”.

These days words do still count and so does the ability to demonstrate a GSOH (it stands for good sense of humour, by the way). But in 2018 the big-boned cage wrestler is also likely to be using dating apps such as Tinder in her search for a sparring partner. And if she is, she's in good company: Tinder alone has around 50 million users worldwide. You upload an image of yourself and then potential matches either swipe left (no thanks) or right (maybe). If two users both swipe right, they can then chat using the app. The rest is up to them.

THE ETIQUETTE OF MODERN DATING

This is where it gets trickier. People have been asking about modern dating etiquette – and being provided with dreadful advice about it – probably since the invention of teenagers in the 1950s. Whether the subject is more or less of a minefield than in previous decades depends on your point of view, but certainly there is more nuance to today's dating scene which suggests it's certainly no easier today than in previous decades.

At least if you're using a dating app you've already established a physical attraction with a prospective partner. In a sense that makes the next steps a little easier, especially as the date itself might come after days or even weeks of serious online flirting (though overuse of punctuation in texts and in-app messages – !!!!! – is a serious don't).

But take a look at how rich, varied, expansive and downright catty even the dating lexicon has become and you realise that minefield doesn't being to describe the half of it. After all, you wouldn't want to be accused of wasting someone's time by “kittenfishing”, especially with “cuffing season” coming up. The first is when your social media profile doesn't quite match up to the impression your real world self makes, the second is the hectic social round that sees desperate daters trying to lock prospective partners into a relationship that will last at least as long as a two week holiday in Magaluf. After that, “clearing season” kicks in and you move on.

There are other even more nebulous concepts to take into account, such as “breadcrumbing” (leading someone on by blowing hot and cold), “benching” (keeping one person hanging on while you look for someone better) and “socialating”, a portmanteau word every bit as thorny as it is hellish sounding. It's a cross between socialising and dating, which means nobody's really clear about what's happening or where the boundaries are. In short, the only thing we can say for sure about modern dating etiquette is this: it's kind of complicated.

FALLING IN LOVE

These days men and women are waiting longer to settle down and have children. Between 1971 and 2017, the average age at which people married rose from 24 to 32 (for men) and 22 to 30 (for women). Among same sex couples, women are far more likely to marry than men. Meanwhile those who have lasted beyond the first date and become a couple also wait longer before marrying, with the average couple waiting around five years. But when they do get hitched, fewer than ever before will do it in a church.

There has also been a recent rise in single person households, with the difference between men and women most stark in the 25-44 age group, where twice as many men live alone. The only age groups in which there are more women than men living alone are the 65-74 and 75 plus groups. In total there are 7.7 million one person households in the UK, according to the Office for National Statistics, though the number of young people living with their parents has also increased.

What does all this mean? More single young people looking for other single young people, basically, which means more dating. Not that these single young people necessarily end up having more sex: a study of 27,000 Americans aged between 20 and 24 found that they were having far less sex than those born in the 1960s were at the same age. Their parents, in other words.

HOW TO HAVE THE PERFECT VALENTINE'S DAY …

The traditional Valentine's Day ritual is a candlelit dinner at a romantic restaurant then home for – well, let's call it dessert, shall we? Other staples include cards and confectionery (we spend £53 million a year on each) and of course flowers, on which we spend a further £102 million a year.

Unsurprisingly, roses are the most popular Valentine's Day bloomers, followed by carnations and lilies. But those wanting to impart a more coded message with their choice of flowers could go for gerbera daisies, which symbolize purity and innocence; tulips, which stand for perfect love; or, for the classicist in your life, fluffy peonies. In Ancient Greek myth, Paeonia was a beautiful nymph who was turned into a flower after Aphrodite caught her flirting with Apollo.

Less traditional than a romantic dinner, perhaps, but almost as popular is a trip to the cinema. It's no co-incidence that Fifty Shades Freed, the third film in the erotic drama franchise, was released on Friday, just in time for Valentine's Day. Though you might find the merman-human love story The Shape Of Water a bit more upmarket.

Or maybe you just want a night in with a curry and a box set of The Detectorists. In fact, lots of people will be doing just that, or something like it. According to market research firm Mintel, food and drink bought to be consumed at home tops the list of Valentine's Day buys, reaching £128 million last year.

Other popular Valentine's Day treats include gifts such as jewellery, or clothing and footwear. We spend £112 million and £80 million on those respectively. The giving of presents is oddly gendered too: 53% of men bought a Valentine's Day gift in 2017, spending an average of £72, compared to 39% of women, who spent £44 on average.

But shoppers of both sexes are now looking for more creative ideas for Valentine's Day gifts, according to retail analyst Samantha Dover. How about an Outlander Walking Tour for two around Edinburgh (Jacobite dress optional), an evening of star-gazing in the Galloway Forest Dark Sky Park and, not for the faint-hearted, a 160ft “Lovers Leap” tandem bungee jump at Glasgow's Riverside Museum. That one comes complete with a complementary half bottle of champers, though you don't get that until afterwards.

Of course, sex toys are increasingly popular, but if there's one present you should avoid this Wednesday it's to be found in Poundland's recently unveiled Valentine's Day range: a £1 vibrator.

FINALLY, WHO WAS ST VALENTINE ANYWAY AND WHY ALL THE FUSS?

The truth is, nobody really knows who Valentine was. The feast of St Valentine on February 14 was established in 496 by Pope Gelasius I, and Valentine is generally reckoned to have been a Christian priest who was martyred and buried in Rome in the 3rd century AD. But he may be actually be a conflation of three different Valentines who all met grisly ends. In one of the versions, Val was imprisoned for carrying out a Christian marriage ceremony - making him the patron saint of lovers.

St Valentine's journey from the pages of the Martyrologium Hieronymianum to the shelves of Clinton Cards becomes a little clearer after the Middle Ages, thanks mainly to Geoffrey Chaucer. His 1382 work The Parlement Of Foules makes an implicit link between St Valentine's Day and mating and in 1400, with the concept of “courtly love” in full swing across the hipper European kingdoms, that link was strengthened further in the Charter Of The Court Of Love. Supposedly issued by Charles VI of France, it laid out the rules for chivalrous Valentine's Day activities such as jousting and (far safer) competitive readings of love poetry.

Fast forward a couple of centuries and we find William Shakespeare, John Donne and Edmund Spenser all mentioning St Valentine's Day. By the late 18th century, British publishers were printing Valentine cards. And pity the poor postmen of the 19th century: in 1840, some 400,000 cards were delivered. Topping even that, the US Greeting Card Association estimates that around 190 million are sent annually in America. That alone is proof of how Valentine's Day became commercialised in the 20th century.

So St Valentine's Day is now big business – bigger even than Easter according to Mintel, which found that spending on the first now outstrips spending on the second by a significant margin. But whether you plan to mark it with a TV dinner for two, an evening of 'Netflix and chill', or a dirty weekend in Brighton (oh for the bad old days of the 80s and 90s) make sure you remember what it's meant to be about at heart: love, kindness and an appreciation of your significant other.