The fashion police will be out in force at this year's Royal Ascot after new dress guidelines were drawn up for Royal Enclosure badge-holders.

Forget your spaghetti-strap, strapless or halter neck dresses if you want to get into the Enclosure, in what Royal Ascot say is not a tightening but more of a "clarification" of the dress code. Shoulder straps should not be less than an inch thick and for headwear, there should be a hat or "substantial fascinator".

What's more, unmatching trouser suits or uncovered midriffs could mean you are turned away from the Enclosure or, if you've sneaked inside, are "relieved" of your Royal Enclosure badge. National dress will be tolerated.

Ascot has long been a chance for the great and good to show off their fashion prowess. But some old-school attendees feel that in some cases hems have got too short and necklines too low.

Nick Smith, a Royal Ascot spokesman, insisted this wasn't an indication that the event was failing to move with the times: "We have got to be very careful with fashion. Ascot has always been a fashion event and we want it to stay that way. However, we want the fashions to be appropriate to a formal occasion, not evening wear. It's a question of toeing the line.”

Mr Smith added that the alteration was not a dramatic leap from previous years: "We have not changed the dress code,” he says. ”It was a bit vague and people like it to be clear. I would be loathe to say that standards have declined, but we were keen to re-establish the nature and spirit of the occasion."

Any offenders will be treated sensitively: "If someone is in breach of the dress code, they will have to go and buy a jacket from the high street. Nobody is going to be marched out."

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