No treasure was found in Bromley last year, despite almost 1,000 discoveries elsewhere in England and Wales.
The Institute of Detectorists said finding treasure gives historians a valuable insight into the past, but encouraged hobbyists to practice "responsible" metal detecting.
However, figures from the Ministry of Justice for 2021 show there were no finds reported to South London Coroner's Court, which is responsible for holding treasure inquests.
This was in line with the year before – though seven treasure troves have been found in the area since records began in 1995.
Across England and Wales, 908 finds were reported last year – 13% more than the year before, but still below the record 1,061 found in 2019.
The Treasure Act, introduced in 1997, defines treasure as discoveries older than 300 years.
These include coins, prehistoric metallic objects and artefacts that are at least 10% precious metal such as gold or silver.
All potential treasure finds are processed by the British Museum, whose experts advise coroners on whether the find fits the definition of treasure.
If a coroner rules that it is treasure, both local and national museums are given the chance to acquire the pieces, and the finder will be paid a sum depending on the treasure's value.
But if the find is determined not to be treasure, or no museums want it, then it is returned to the treasure hunter.
The MoJ said the number of finds increased steadily from 1997 but since 2018 the trend has been more volatile.
It said the rise in the number of finds from 2020 to 2021 is likely due to the easing of coronavirus pandemic restrictions.
With 87 finds, there was more treasure found in Norfolk last year than anywhere else across the two nations.
The MoJ said the number of finds varies greatly across the country, most likely due to "geographical and historical differences" between areas.
Keith Westcott, founder of the Institute of Detectorists, said: "Beyond the fascination which surrounds treasure and monetary rewards, is an important value of detecting finds – a historical value which provides a valuable insight into our past.
"Often though, the archaeological record which surrounds the find, the information that gives it context, is damaged or ignored."
He encouraged amateurs to follow responsible metal detecting and leave important finds n place ready to be excavated by archaeologists.
He said a recent example of this was when amateur detectorist Mariusz Stepien stopped digging upon realising he had discovered important objects in Scotland in 2020, allowing archaeologists to recover a rare haul of Bronze Age artefacts.
Anyone who discovers something they think is treasure must report their finding to the coroner within two weeks, so the court can hold an inquest to decide who should get to keep it.
Failure to do so can result in an unlimited fine or up to three months in prison.