Producers were keeping light-lipped about the nature of the item, which was brought by a member of the public to Harrogate’s Royal Hall yesterday.
Its value is said to be higher than the programme’s previous biggest find - a model of Antony Gormley’s Angel of the North statue, which was valued at £1m in 2008.
A spokesman for the show said the Harrogate find was “a world-famous piece owned by a sporting institution.”
He added: “The final valuation given will be revealed when the programme airs in Spring 2016.”
More than 2,500 people queued for up to 90 minutes to have their family heirlooms, household treasures and car boot sale bargains inspected by the experts in Harrogate.
Among them was the Yorkshire Challenge cup, held by Harrogate Rugby Club and worth around £20,000.
Graham Siswick, Team Manager for the club discussed the cup’s history with the experts.
He said: “Harrogate Rugby Club hold the trophy at the moment, they won it last season so we thought it might be appropriate to bring it along. It’s supposed to be the oldest rugby trophy in the country.
“The club was founded in 1871 but the cup was played for for the first time in 1876.”
His wife Jennifer added: “It was 50 guineas when it was bought. It’s the only one of it’s kind so you can’t buy the providence. It was just interesting to know what that 50 guineas had multiplied into.”
Another visitor, Cathy Bryant from Knaresborough, brought postcards, more than 100 years old, sent from her great grandfather during the First World War.
She said: “My great grandfather died in the Somme in 1915 and he sent these postcards to his wife when he was over there.
“I just thought it would be interesting to find out what the pictures were and why they chose those pictures on the postcards.”
Fiona Bruce, Antiques Roadshow presenter, said: “This will be my 8th year on the Antiques Roadshow and I still feel so lucky to be presenting the programme. Every week is different; a new location and thousands of new visitors. The only constant is the pleasure of the unexpected - we never know what will turn up, from the most fabulous Faberge to the most humble object with a riveting story.”
During the last series the Antiques Roadshow unearthed some amazing finds including a Chinese enamel box bought for 20p and valued by the experts at over £10,000.