Princess Eugenie skirts close to the wind at superstrict Royal Ascot with her risque hemline

But they were prepared to make an exception for one young racegoer in a dress several inches above the knee  -  Princess Eugenie.

The 18-year-old younger daughter of the Duke of York chose a flirty white studded Collette Dinnigan frock for her day at the races, teamed with a purple feathered Philip Treacy hat and matching boxy jacket from the Chelsea boutique Arrogant Cat.

Looks like I got away with it, Bea: Eugenie in her thigh-skimming, rule-breaking dress, with sister Beatrice at Ascot yesterday

Skirting the issue: Eugenie in royal purple with sister Beatrice and Sophie, Countess of Wessex

Royal Ascot spokesman Karen Smith claimed not to have seen the dress, but added: 'As long as it is not a miniskirt and is in keeping with the rest of the outfit then the wearer would be allowed into the Royal Enclosure.

'The idea that hemlines must be no more than two inches above the knee is a bit of an urban myth.'

Eugenie was accompanied by her sister Beatrice, 19, in black-and-white Alexander McQueen suit.

Their cousin Zara Phillips chose a cream blouse with high-waisted, fifties-style black skirt.

The international equestrian, who has had to withdraw from the Beijing Olympics because of an injury to her horse, shared an enthusiastic hug with her uncle Prince Charles in the Royal Box.

Royal Ascot's new dress code, which also bans bare midriffs, was imposed following a tendency to ever-more daring outfits.

Eugenie was not the only woman to make an effort with her outfit as witnessed by the many women in attendance at the five day racing event.

The three fashionable minor Royals were joined by the Queen, Princess Anne and the Countess of Wessex, who all opted for pastel outfits.

The Duchess of Cornwall wore a pale mint green dress suit with a matching feather-trimmed hat.

The event also attracted a host of celebrities including Michael Owen and his wife Louise, music mogul Andrew Lloyd Webber, Judi Dench and Nigel Havers.

For the first time this year the prize money on offer to jockeys over the course of the five-day meet in Berkshire has reached £4million.

But those betting on the outcome are likely spend at least half as much on champagne.

Back to the fifties: Zara Phillips, the Queen's granddaughter in high-waisted skirt and blouse with a bow

Pale and interesting: The Queen and Camilla, The Duchess of Cornwall, arrive at the five day event

Last year 170,000 bottles were bought by thirsty punters at a cost of just under £2million.

They also managed to consume 10,000 lobsters, 5,000 oysters and 18,000 punnets of strawberries in between races.

Helping hand: Zara Phillips shares a joke with diminutive ex-jockey Willie Carson

Princesses Beatrice and Eugenie clearly enjoyed the day with Beatrice (right) happily cheering on the horses

Mwah, mwah: Zara kisses her uncle Prince Charles on the cheeky

The Queen and members of the Royal Family will join the thousands of racing fans on each day of the event.

Their arrival, in horse-drawn carriages before the first race of the day, amassed a  large crowd.

Those privileged enough to be in the Royal Enclosure, which maintains a famously strict admittance policy, will have to keep their eye on their outfit this year.

Suited and booted: Michael Owen, Andrew Lloyd Webber and Nigel Havers in morning dress

After confusion over the definition of 'formal day dress' in 2007 the Ascot authorities have reworded the dress code for women.

In now states: 'For ladies, only formal day dress with a hat or substantial fascinator will be acceptable.

'Off the shoulder, halter neck, spaghetti straps and dresses with a strap of less than one inch and/or miniskirts are considered unsuitable.

Turning heads: Jodie Sykes, left, and Florence Claridge's hats attract attention

Midriffs must be covered and trouser suits must be full length and of matching material and colour.'

For men the matter is somewhat simpler. Morning dress including waistcoat and top hat is the only permitted attire for the top-level of enclosure at the course.

Racegoers in other parts of the course, where the dress code is more relaxed but still demands formal-wear, often make as much of a sartorial effort as those in the Royal Enclosure.

Racegoers arrived in all-manner of exotic head-wear

The third day of the meet often sees the most spectacular outfits and has become know, as Ladies Day.

Female racegoers have an extra incentive to dress up this year as scouts from modelling agency, Models 1 and the Sunday Express's S Magazine will be looking for the new face of the racecourse.

Colour coordinated: This group of ladies from Gloucester were clearly leaders in the Having A Jolly Good Time Stakes

...from the front and the back

Jackie St Clair, left, and Rebecca Branwell strike a pose

The search will take place within the public enclosures on the opening two days and shortlisted candidates will be invited back on the final day of Royal Ascot, Saturday, to present the trophy for the last race.

Blooming outfit: Racegoer Henrietta Aitken is underneath this hat