LONDON - AN IRON ball and chain found on the banks of London's River Thames is causing a stir amongst archaeologists who say the 300 year-old artefact used to restrain convicts on ships may have a gruesome story to tell.

The prospect conjures up a tantalising tale reminiscent of the work of 19th century Victorian author Charles Dickens, said Museum of London archaeologist Kate Sumnall who examined the find.

'Whether a real-life 'Magwitch' freed himself from the 'great iron on his leg', or perished in shackles, or whether this ball was simply discarded, we can never know,' she said.

Abel Magwitch is a character in 'Great Expectations' - a violent convict who escapes from a prison-ship.

'Nothing like this has ever come across my desk before,' Dr Sumnall said, adding that to find a complete set of irons was very rare.

She said the fact that the device is made of high quality iron made it very valuable at the time suggesting that it was unlikely to have been discarded. 'And we also know from the lock design that it was not a slave ball and chain,' she said.

The padlock is skilfully made with the screw-thread carved after the padlock had been cast. English padlocks of this time were not made in this way suggesting it was made somewhere in continental Europe, possibly Germany.

The long spike on the padlock would have pointed towards the other leg when it was fitted around the ankle, Dr Sumnall said.

The device, which weighs 8 kgs, has been preserved by the thick black mud of the Thames whose anaerobic properties protect metal, ceramic and even leather finds exceptionally well. -- REUTERS