Shrove Tuesday is the day before the start of Lent, a period of 40 days leading up to Easter in the liturgical calendar. In Lent, Christians practice self-denial to commemorate the 40 days Jesus spent fasting in the wilderness in preparation for his ministry. Traditionally that meant only one meal a day - with no meat or products from animals including eggs, butter and milk. Since the Reformation, the practice of fasting has gradually been replaced by an emphasis on giving to charity.

So why pancakes?

On the day before Ash Wednesday, families used up all the products they would not eat in Lent. Pancakes were a dish that could use up all the eggs, butter and milk in the house with just the addition of flour. A pancake was, in those calorie-starved days, considered a luxury, as this 16th-century poem showed:

"Then there is a bell rung, cal'd the Pancake-bell, the sound whereof makes thousands of people distracted, and forgetful either of manners or humanitie; then there is a thing called wheaten floure, which the cookes do mingle with water, eggs, spice, and other tragical, magical inchantments, and then they put it by little and little into a frying pan of boiling suet. . . until at last, by the skill of the Cooke, it is transformed into the forme of a Flip-Jack, cal'd a Pancake, which ominous incantation the ignorant people doe devoure very greedily".

Is this custom peculiar to the British?

No. The custom of eating pancakes at Shrove Tuesday is popular in many parts of the world - from Lithuania to the Philippines, where they are made from rice flour and topped with white cheese, butter, sugar, salted duck's egg and coconut. Others have confections based on the same ingredients. In Scotland, today is called Fasten's E'en, or Bannocky Day in reference to bannocks of eggs and meal mixed with salt and baked on a gridiron. The Swedes have something called fastlagsbulle, a sweet bun filled with almond paste and whipped cream, served with hot milk. The Germans have fasnacht, a diamond-shaped, yeast-raised potato pastry that is deep-fried like a doughnut. The Italians have a pastry baked in the shape of a dove called a columba.

So where does the sex come in?

Elsewhere, the farewell to flesh (for which the Latin vale a carne became carnival) took slightly more exotic forms such as the excessive indulgence of the Mardi Gras carnival. Mardi Gras is French for Fat Tuesday, a reference to a key pancake ingredient, but flesh takes on a wider meaning than mere meat-eating.

In Poland, where the pre-Lenten fare is pickled herring and vodka, as well as paczki donoughts, young men would buy back their sweethearts during the traditional Shrove Tuesday auction sale of girls, after which the young woman would be taken to a byre, placed in a manger full of hay, and a careful physical examination was given - including, it was said, her teeth. In England, on Shrove Tuesday there was dice and card playing, mumming and revelry. Wagons were decorated with hundreds of bells. Apprentices were given a holiday.

What was eaten when the pancakes were all gone?

Fish. Church rules, like those of many self-styled vegetarians nowadays, ruled that fish was not meat. In the Middle Ages meat, eggs and milk were forbidden, not just by church rules but by legal statute. Entries in the royal household accounts of Edward III show that fish was the chief Lenten fare, with herring-pies a great delicacy. Charters granted to seaports often stipulated the town should send a set quantity of herrings to the king annually during Lent. After the Reformation, Protestant politicians preserved the rule because it was good for the fishing industry, which was the cradle of England's maritime prowess. Though later the Puritans, like many modern schoolchildren, ostentatiously avoided fish as a sign of their militant Protestantism.

Why is it a different date each year?

Since Easter is a moveable feast, so is Pancake Tuesday. It is always 41 days before Easter Sunday. There have been bitter arguments over the date of Easter for centuries. Asia was excommunicated for several centuries for heresy over the date. Christians in England were split over it for decades. It was finally fixed by the Council of Nicaea in AD 325. The day chosen was the Sunday following the first full moon after the spring equinox - the day of maximum light with 12 hours of daylight, followed by 12 hours of full moonlight.

In 1928, the House of Commons agreed to a bill fixing the date as the first Sunday after the second Saturday in April, but it was never implemented. In 1990 the Vatican approved a proposal for a fixed date but all the other Christian churches, and world governments, could not agree. Easter is just about as early as it can be this year - 22 March is the earliest and this year it is 23 March. So Pancake Day is unusually early too.

Are pancakes the only remnant of this tradition?

Pretty much. Various towns also have traditional pancake races. One of the oldest is at Olney in Buckinghamshire, where competitors have made a 415-yard dash from the old coaching inn to the parish church since 1445 - each tossing a pancake at least three times en route. Westminster School in London has its annual Pancake Greaze, in which a master tosses a massive pancake over a 15-foot bar and the pupils scrabble for the prize.

Most of the other traditions have gone. Cockfighting was a regular Shrovetide activity, though it was prohibited as early as the reign of Edward III. Many places also had a shriving bell rung to call people to confession. It became the signal for housewives to prepare their pancake batter for lunch - and for children to leave school for a half-day holiday.

What about Pancake Day football matches?

These live on in some locations - most famously Alnwick, Ashbourne and Atherstone - and date back as far back as the 12th century. But the Highway Act 1835, with its ban on playing football on public highways, killed most off, much as the self-denial of Lent has been replaced by a modern hedonism broken only by a post-Christmas slim, and, increasingly, a self-imposed alcohol ban, through the month of January. Perhaps Pancake Day is now just the sign that the slimming is over.

Mark Hix's perfect pancake recipe (Serves 4)

> 120g plain flour, sifted

> 1 medium-sized free-range egg

> 1 teaspoon caster sugar (for sweet fillings)

> 300ml milk

> A little vegetable oil for frying

Whisk flour and egg, and sugar for a sweet pancake, with one third of the milk until smooth. Whisk in remaining milk, then strain if needed. Heat a non-stick frying pan, rub with a little vegetable oil, then add a little of the batter. Tilt pan immediately so the mixture is even and thin. After about a minute, when the pancake is lightly browned underneath, turn it with a spatula or palette knife - or toss it. Cook for another minute, until lightly coloured underneath, then turn out and serve.