A blue vase spotted by a couple ambling round a flea market has turned out to be a rare - possibly unique - antique worth hundreds of pounds.

The lucky pair paid £30 for what has turned out to be a 'lost piece' of century-old Loetz glassware. And such is its importance it could sell for 14 times the price they paid when it goes under the hammer at Melbourne's Irita Marriott Auctioneers next month.

The vase, believed to be the only known piece of its kind in existence, was previously unrecorded on the Loetz database. However, thanks to an identification (DEK) number on its base it has been confirmed as genuine.

It was discovered by a 46-year-old Essex builder's merchant foreman and his partner during a weekend stroll. He said: "We went to a flea market in South Yorkshire on a Sunday morning earlier this year. It's something we very much enjoy along with car boot sales and antique shops.

"We mainly like to buy glass. We were having a good look around when we came across a stall with some lovely vases and studio glass. Among numerous items on display was a gorgeous blue vase with white enamelling.

"We picked it up and inspected it for any chips or cracks then looked at the bottom. It displayed various numbers and letters. The stall holder said we could have it for £30 so we bought it. Once home we got Googling to try to identify it. We thought it was Loetz glassware but we were a bit baffled as we couldn't find anything like it.

"We took a photo and put it on a Loetz collectors' page on Facebook. Somebody said it could possibly be a new DEK number. Loetz assigned a DEK number for each unique decoration pattern. We were very excited and emailed photos and details to renowned Loetz specialist Deb Petersen Fitzsimmons. We were thrilled when she confirmed it was a true Loetz with a new DEK number.

"We haven't used it, just kept it safe. It really is beautiful and the enamelling is exceptional. It would look gorgeous within a collection. We told antiques expert Irita Marriott about our find and she was really excited so we decided to consign it to auction with her. It's nice to think a £30 flea market find could earn us a windfall."

Irita, a popular face on TV's Bargain Hunt, Antiques Road Trip and Celebrity Antiques Road Trip, said: "When I was first told about this vase I was really excited. Who wouldn't like to find, handle or sell a piece no one else has had a chance to discover? This is one of the missing Loetz pieces.

"There are quite a few images missing for various Loetz items on the firm's database. They have the numbers so they know they exist. However, this vase was not on the Loetz database at all. Nevertheless, from the numbers on its base they could identify it as one of theirs. It has been confirmed that it is not a fake but indeed a true Loetz. The vase's DEK number has now been added to the Loetz database. Lost Loetz items come to light occasionally but usually their DEK numbers are already known.

"This stunning vase was made in the period Loetz refers to as DEK (1888 -1912) which makes it more than 100 years old. It isn't a classic Loetz look but still has the magical iridescence their pieces are known for. This is perfect for a Loetz collector who wants to own something different, beautiful and potentially unique.

"It will be offered in the inaugural sale at my new Derbyshire auction house on January 11. I am guiding it at £200-£400. Loetz glassware is highly desirable with collectors all over the world. It's nice to think this piece was found at a flea market by a couple who simply like coloured glassware. It goes to show forgotten antique treasures are still out there just waiting to be discovered."

Austrian Johann Loetz Witwe was an important art glass manufacturer in Klostermühle, Bohemia, Austria-Hungary. He founded his glass company in 1842 by acquiring the Goldbrunn glassworks. After his death in 1844, his widow Susanne renamed the company Johann Loetz Witwe. The glassware is renowned for its quality, innovative techniques and metallic iridescence. Loetz works are among the most outstanding examples of Art Nouveau.

Auction: The Loetz vase, lot 491, will be offered in the January 11 Antique and Collectors Auction at Irita Marriott Auctioneers and Valuers, Melbourne, Derbyshire.