More than 400 people turned up with their collectables at the ground to meet TV's Flog It valuers.

Among the hidden gems was one of the show's most valuable finds – the 1641 passport, which has been valued at up to £20,000.

The document was brought to the event by Peter and Eileen Milner. It had been bought as a present for Mrs Milner for about £100.

Mrs Milner said: "It has beautiful writing with the signature of Charles I, we believe, and it gives passage to a Captain Bradshaw and his wife and servants to travel the oceans on behalf of the king.

"It is fascinating – it belonged to a friend of ours who was a collector and when his estate was being sold my husband bought it for me as a birthday present.

"It may go for from £2,000 to £20,000. We just don't know until the day of the auction.

"It would be nice if it went to a museum or the Passport Office if they have collections. But for the moment it is with the BBC for safe-keeping."

Crew from the hit BBC2 show were in Sunderland to film for their forthcoming autumn series.

Presenter Paul Martin said: "It's just flat out here. We have been so busy, but we have seen some fantastic things.

"I'm really excited about the passport from 1641, which is signed by Charles 1.

"The owner has had it in their possession for about 10 years.

"We checked with the passport office and it is the oldest they have on record."

Members of the public are invited to bring along antiques and collectables as part of the popular show, which regularly attracts about two million visitors.

Once the item is valued, the owner and a team of experts decide whether it should go forward for auction.

Previous programmes have discovered a Royal Doulton tugboat, bought for 50p which achieved £360 at auction and a microscope found in a skip which sold for £1,300.

Paul said it was the unpredictable nature of the show which is key to its success.

"You just never know what is going to happen," he explained. "It's the fear factor, the surprise factor and the human element which makes Flog It such classic viewing."

Everyone who turned up on the day had their items valued, but only a select few were chosen to be filmed for the show.

Collectables brought along to the event ranged from musical instruments to jewellery, pottery and fine art.

Those items earmarked for auction from yesterday's filming will go to Boldon Auction Rooms to go under the hammer on Wednesday, June 3.

Paul added: "We always get a good reception here.

"Everyone is really warm-hearted and has a great sense of humour, which makes for great TV."

Find out more about the hidden gems unearthed during Flog It's visit to Sunderland in tomorrow's Echo.