The buckle, left, from the 7th or early 8th century, was gilded in gold or tin, and would have glistened so much that its wearer was sure to be noticed. It goes on display at the Museum of London today.

The site, possibly a Saxon grave, cannot be disclosed until archaeologists have been able to excavate the area, which could be a grave site.

The discovery demonstrates London’s long history as a hub for migration. The buckle, a copper alloy with a Byzantine design, would usually be found in what is now southern Spain or Portugal.

It is, therefore, a Hispano-Visigothic object. “It is beautifully incised,” Faye Simpson, of the museum, said. She added that it would have been worn with other, equally magnificent, jewellery.

The finder was Bill Robson, a retired Londoner in his fifties, who goes out every week with his metal detector, and then approaches the museum with his finds.

Ms Simpson said: “He has found nothing quite as impressive as this.”

Explore UK News

• Crime News

• Education News

• Health News

• Science News

• Scotland News

Times Recommends

• 'Ghost bus' runs to spare ministers' blushes
• Mobile phones finally passed fit for hospitals
• £6m of sick miners' awards went to union