A RARE magnum of champagne to celebratate the 1981 marriage of the Prince and Princess of Wales is to be auctioned in Swindon.

The large bottle of Cuvee Dom Perignon 1961 the year was chosen because it was the year of Diana's birth is expected to raise at least £1,000.

It will be sold alongside other royal memorabilia at Dominic Winter Book Auctions in Maxwell Street on December 15.

Auction house valuer Chris Albury confessed that putting a price on such a piece was difficult, and that it might eventually raise £3,000 or more.

He explained: "The market for items related to the princess is always highly unpredictable.

"There is always media interest in her, but collectors are more hesitant because it still a very volatile market.

"Nobody really knows for sure whether she is a solid investment, or whether she is going to fluctuate."

The magnum is being sold by Luton man Brian Minningham.

Mr Minningham, a pub landlord who is retiring, bought the bottle in 1987 for £100.

He came across it while clearing out his cellar.

Mr Minningham said that the bottle was in pristine condition, having been removed only once from its commemorative box.