The magnum is believed to be one of only 12 ever produced

The magnum is believed to be one of just 12 of 1961 Cuvee Dom Perignon produced by Moet & Chandon.

Retiring pub landlord Brian Minninghan, of Luton, Beds, who paid �100 for the bottle in 1987, found it as he cleared the loft of his pub in Slip End.

It goes under the hammer on 15 December at an auction in Swindon, Wilts.

Valuer Chris Albury, of the Dominic Winter auction house, said: "My current valuation is at least �1,000 but whether we will list it at �2,000 to �3,000 will be decided nearer the time. Who knows what it might fetch on the day?"

Mr Minnighan, 67, said: "I was clearing out the loft and there it was. We decided to get rid of it.

"It's in its original box that has only been opened once since I bought it. I'll miss it."

'Incredibly rare'

The Cuvee Dom Perignon 1961 vintage was selected as it was the year of Princess Diana's birth.

At the time Moet & Chandon said as the quantity available of the "incredibly rare" Cuvee was so small it was not offered for sale.

It is understood that just 99 bottles and 12 magnums of the vintage were shipped across from the France for the wedding.

Moet was unable to verify the exact number of bottles and magnums produced for the wedding but a spokesman said: "It is incredibly rare. The 1961 is not available any more."