More than 50 million red roses will be given away on Friday - but none must arrive at the wholesaler before Wednesday. The price will rise sharply, and could even double, but that will not ensure supply meets demand and many loved ones will go out without. Frustrated men might then ponder a new Hamilton Direct Bank survey, which shows that what women really want for Valentine's Day is a car or a horse.
Valentine's Day is the focus of the romance industry, which is dwarfed by the sex industry but is still significant. The day itself generates about pounds 50m in extra business for UK commerce. The romance business as a whole is worth something over pounds 1.5bn.
Were Valentine's Day at another time of year, it would be less important. It is the first excuse to spend money after Christmas, and comes at a time when many people feel ground down by the long winter. "It's the first big eating-out day after New Year's Eve," says Peter Conway of the Restaurateurs Association of Great Britain.
But it is nothing like as big here as in the United States. In Britain Valentine's Day is still, mostly, to do with romance - couples are extra sloppy, singles are extra depressed. In the US it is more to do with mothers and classmates. The growth in card sales here may reflect some adoption of these ideas - but it is a mercifully slow process.
So how does the romance industry break down? Here is a guide. Some of the business is pure Valentine's Day, some is year-round.
Total sales of cut flowers are pounds 1.2bn, according to the Flowers and Plants Association (FPA). About 65 per cent are gifts, so if we guess that a quarter of the gifts have romantic connotations, we can say the Byronic flower market is worth about pounds 200m.
Valentine's Day is big for the flower sellers, causing a 32 per cent rise on average. But it is not as important as Mother's Day (76 per cent) because, as Veronica Richardson of the FPA says, "even mothers have mothers".
The problem is not volume but the concentration on one type of flower: the red rose. About 7 million, costing pounds 22m, are sold in Britain. "We just can't produce enough of them for that one day," Ms Richardson says. She would like buyers to discover the delights (and cheapness) of orchids, lilies, even daffodils.
But red rose demand continues to grow, and the only thing stopping a stem being worth its weight in gold is the expansion of growers. Holland and the Channel Islands were joined by Israel and Colombia 30 years ago; now roses come in from Kenya, Zimbabwe, Zambia and India.
Although newspapers carry pages of Valentine ads, the effect on revenues is marginal: perhaps pounds 200,000 extra. The occasion does, however, give ad agencies an opportunity to exercise their little grey cells: Alliance & Leicester claimed this was "a perfect day for making a change" by switching to its mortgage.
Valentine's cards are not a big part of the business, but they are growing strongly. John Condon, buying director of the specialist retailer Clintons, thinks the market grew by about 6 per cent in 1996, compared with 2 per cent overall growth. The Post Office predicts a record 11.2 million cards will be sent this week, against 10.5 million last year.
Of the 2.4 billion cards bought in Britain last year, the Greetings Cards Association (GCA) reckons that 62 per cent were for Christmas and only 1 per cent - 22 million - for Valentine's. However, only the bold bulk- buy Valentine's cards, which is why their average value, pounds 1, is five times higher than for Christmas cards. Their value was thus pounds 22m in a total card market of about pounds 1bn.
The traditional unsigned "I love you" card is now being replaced by more offbeat, witty or smutty offerings, says Mr Condon. "What is acceptable on cards seems to be increasing all the time." A big card shop may have 20,000 Valentine's cards on display, but only a handful will be in the American vein - "To my Aunt on Valentine's" - and these will be bought by US expatriates.
Can card companies "create" new days to sell more cards? "Not in Britain," says Ray Cousins of the GCA, pointing out that Grandparents' Day was a resounding flop.
According to the retail consultancy Verdict, the ring market in 1995 was worth pounds 725m, "neckware" pounds 350m, ear-rings pounds 250m and bracelets pounds 130m. At least half this, say pounds 800m, must be romance related. Valentine's Day plays its part in this; it is the third most important occasion for selling real jewellery, after Christmas and birthdays.
The chocolate market last year was worth pounds 3.4bn. Of this boxes of chocolates brought in pounds 625m and "chocolate novelties" accounted for pounds 150m. If a quarter of the boxes and novelties had romantic intention, this would put the love-linked chocolate market at about pounds 200m a year.
Two years ago BT did a survey that showed one in five adults planned to phone a loved one on Valentine Day. It did not, however, monitor day- by-day use to see if its predictions were born out. It is certain that the effect in the UK is minute compared with that in the US, where Valentine's Day is an excuse to give mothers, children, pets, anybody a call. AT&T says Valentine's Day is the third busiest in the year for collect calls, suggesting "mom" is often the target.
The dirty weekend has been replaced by the romantic short break. The Association of British Travel Agents says the package holiday business is worth pounds 6bn-pounds 7bn, and guesses that 10 to 15 per cent of this is young couples going away on short breaks. If half of these count as romantic, the market must be about pounds 300m.
Some companies use Valentine's Day as an excuse for selling holidays. Argo is offering a romantic package on Cyprus, "the island of Aphrodite", for pounds 279 per person.
Valentine's Day is a useful top-up for the industry during a dead season (skiing apart), but its effect on the short-break market is probably marginal.
Valentine's Day should be a good time for restaurants: tables for two are booked up well in advance and a special (and specially-priced) menu is usually provided. But according to Joel Kiffin, managing director of Conran Restaurants, there is not necessarily any increase in volume. "It's easy to fill your tables for two," he says, "but how do you fill tables for four or six?"
No Valentine's effect here, but the dating business is a keystone of the romance industry. Frances Pyne, of Dateline and the Association of British Introduction Agencies, says it is growing by 5 to 10 per cent a year. The ABIA has about 100,000 people signed up, at a very rough average of pounds 60. Adding non-ABIA subscriptions, we can guess the industry's turnover is pounds 8m.
Growth is driven both by the high divorce rate and an increase in workload. "Dating agencies mean people don't have to hang around in a wine bar for three weeks and then find out that the person they are interested in is married," Ms Pyne says.
There are about 90 agencies in Britain, ranging from Dateline with 37,000 members to one-man bands. An important segment is specialist agencies serving vegetarian, ethnic or other markets.
The big problem for agencies is the conflict between demographics and equal opportunities. There are four times as many single women over 50 as there are single men, but it is illegal to discriminate by age in an advertisement. Agencies cannot refuse to take an ad from a woman of a certain age, or make special offers to persuade men to join, yet they must have a balance of sexes on their database. "All we can do is tell a woman we'll try it for two months and give a refund if it doesn't work," Ms Pyne says.
The UK's romance industry
Flowers pounds 200m
Cards pounds 22m
Travel pounds 300m
Jewellery pounds 800m
Chocolates pounds 200m
Dating agencies pounds 8m
Total pounds 1,530m