The Royal Ascot races have brought in a strict new dress code including a ban on "fascinators", the tiny hats beloved of Prince William's wife Catherine and other celebrities, organisers said.
Following criticism that sartorial standards have dropped in recent years for the pinnacle of the English social calendar, a team of specially trained dress code assistants will be at the gate to help.
Waistcoats, ties, pashminas and other items will be available at the turnstiles for the annual event which starts on Tuesday in case any of the 300 000 expected racegoers are not properly attired.
"Ascot is Europe's flagship race meeting and one of the world's greatest sporting and social events," said Charles Barnett, chief executive of Ascot.
"We have tried to provide an appropriate dress code that is clear, workable and in line with the wishes of racegoers.
"During the meeting itself, our team of special dress code assistants will help people with any queries that they may have."
The new dress code was first announced in January and organisers sent out reminders with badges and tickets this week for this year's races at the course in Berkshire, southern England.
A particular stipulation is that in the royal enclosure, from where Queen Elizabeth II and other top guests watch the races, fascinators are no longer acceptable.
"Hats should be worn; a headpiece which has a base of 10 centimetres or more in diameter is acceptable as an alternative to a hat," the rules state.
Women are expected to wear skirts or dresses of "modest length" falling just above the knee or longer. Men must wear black or grey morning dress with a waistcoat and tie, a black or grey top hat and black shoes.
The rules in the grandstand are less stringent but women must still wear a hat or fascinator, and strapless or sheer-strap tops are banned. A suit and tie are compulsory for men.
Last year an unseemly punch-up on Ladies Day at Royal Ascot triggered concerns that the event was becoming overrun with vulgar "riff-raff".
With Queen Elizabeth II in attendance at the racecourse, an ugly brawl erupted, with drunk punters swinging fists, table legs and even £100 bottles of champagne at each other.