The gown, by Alexander McQueen designer Sarah Burton, will take centre stage. It will be the first time the ivory and white satin gown and 9ft train will have been seen in public since Kate Middleton married Prince William at Westminster Abbey on April 29.

The Duchess’s dress will be displayed from July 23 until October 3 in the  palace ballroom — the grand room that was used for their wedding reception and which is the setting for investitures.

Her handmade shoes, diamond earrings - a present from her parents - and the Halo Tiara she was loaned by the Queen will also be on show.

The eight-tiered wedding cake made by Fiona Cairns will be also on display in the State dining room. The other cake — a chocolate biscuit cake made by McVitie’s to a special recipe from Prince William — was believed to have been eaten on the wedding day.

The exhibition will be open seven days a week but many weekend slots are already taken. More than half a million people are expected to visit, paying £17.50 a ticket, breaking the previous highest attendance figure of 420,000 in 1994.