A slice of toast - left over from Prince Charles' breakfast table on the day he married the late Princess Diana - has sold at auction for 230 pounds (NZ$450).

The humble scrap was kept by a former servant of the palace as a memento of the 1981 wedding, which was watched by 750 million people worldwide.

Rosemarie Smith, whose daughter worked for the royal family for nearly three decades, described how the bread, which was kept on her shelf in a cup, came to be in her possession after a visit to the palace on the day.

"At the time my daughter was a maid at the palace and one of her duties was to collect Prince Charles' breakfast tray from outside his room," she said in a press statement.

"I was with her in the corridor and saw that Prince Charles had left some toast on the tray. I had been thinking about a keepsake from the wedding and saw the toast and thought to myself: 'Why not'?"

The toast was sold by auctioneers Hansons to a UK buyer. It was a record for a piece of toast, whose royal connection helped make the lone slice one of the most valuable food items ever sold at auction in the UK, a spokeswoman said.

There is however no way to prove the toast was from Prince Charles' wedding table, Hansons confirmed.

Smith said she decided to sell the piece after she saw a surge in national pride following the wedding of Prince William and Kate Middleton and the Queen's Jubilee.

"We hadn't talked about it much down the years but William and Kate's wedding last year and then the Queen's Jubilee has made the royals more popular than ever. That got me thinking that my toast could be worth a bit of money," she added.

"I just wandered into the auctioneers out of curiosity and asked them if it was worth anything. I was pleasantly surprised to hear them agree with me that it could be of quite some value to royal collectors."

- Reuters