Diana's spare wedding dress for sale

It is expected to fetch more than £50,000 (€73,500) when it goes under the hammer next month through Cooper Owen auctioneers.

The duplicate dress was made by designers David and Elizabeth Emanuel as a back up.

A spokesman for Cooper Owen said: “The only difference is that the actual wedding dress had Queen Mary’s lace sewn on to the front.

“It was made in case of any hick-up or disaster.

“£50,000 is the reserve price. We expect it to go for a lot more.”

Queen Mary’s antique was the “old” part of the tradition of a bride wearing something old, something new, something borrowed and something blue.

More than 500 million TV viewers around the world watched Diana marry the heir to the throne on July 29, 1981.

The original taffeta gown is kept at an exhibition dedicated to the Princess at her childhood home Althorp.

Cooper Owen creative director Louise Cooper said: “Princess Diana was – and still is – an icon to millions, and we will ensure her legacy is maintained in an appropriate way.”

A replica of the wedding dress worn by the Duchess of York, which was also a stand by, is also being auctioned. It is expected to fetch around £6,000 (€8,823).

Other items being sold include a blue tracksuit which belonged to John Lennon, priced at around £15,000 (€22,000).

He and Yoko Ono wore matching versions of the running suit at a photocall in 1970 to show they had cut off their long hair.

The vest worn by James Dean in the movie Giant is expected to go for around £30,000 (€44,124).

A grey pin-striped suit which belonged to Winston Churchill, Queen Victoria’s black silk skirt and bodice, and a blue and turquoise Pucci dress which belonged to screen goddess Marilyn Monroe are also on sale.

The auction will take place on December 7 at the Proud Gallery Camden in north London.