A dinner plate taken along to the BBC's Antiques Roadshow as an after-thought has turned out to be a £100,000 record-breaker.

Wendy Jones took the 22-inch meat dish from an old Tesco carrier bag and placed it before a stunned expert on the BBC show.

It was then identified as one part of a 100-piece service commissioned for Frederick the Great of Prussia 260 years ago.

The service was made in China and presented to the king by the Prussian East India Company, which he had founded in 1750.

The stunning valuation transformed a previously overlooked object into the most valuable plate ever to appear on the show.

Afterwards, Mrs Jones revealed the journey from overlooked crockery to crock of gold had been a rocky one. The dinner plate had sat on a rickety sideboard in her west Wales home for years - even surviving unscathed when it fell off its stand.

"I only went because my husband wanted to take some books," Mrs Jones said.

"I grabbed the plate and put it in a single Tesco carrier bag - and they can easily split. When I heard how much it might be worth I was shocked. We had no idea it was worth anything. I was left speechless."

She said the plate actually belonged to her son who had left it in Wales because he did not have room for it in his London home. It had been left to him by his paternal grandmother who had married into a German family, which is assumed to have been how it made its way to Wales.

A spokeswoman for the Antiques Roadshow said the unexpected find was the highest value ever for a plate in the show's 30-year history.