Two Kent divers have today admitted failing to declare artefacts worth more than a quarter of a million pounds they plundered from shipwrecks.

David Knight and Edward Huzzey, both from Sandgate, raided ships and illegally kept seven bronze cannon from the wreck of a 19th century British merchant ship in the English Channel.

The pair also targeted the shipwrecks of German submarines from the First World War and an unknown 200-year-old wreck carrying English East India Company cargo.

Their haul also included three propellers from German submarines, lead and tin ingots as well as other artefacts.

The Maritime and Coastguard Agency, which said the value of the items is more than £250,000, said diary entries reveal Knight and Huzzey used explosives and sophisticated cutting equipment to free wreck material.

Knight, a 51-year-old roofing contractor and marine businessman of Castle Road, and Huzzey, a 55-year-old seafood technician of Granville Parade, admitted a total of 19 offences between them under the Merchant Shipping Act.

Under British law, finders of lost underwater treasures have a legal duty to inform the MCA and deliver the items to the authorities if requested.

Alison Kentuck, the MCA's receiver of wreck, said: "Our message is clear: all wreck material found within or brought within UK territorial waters must be reported to the receiver of wreck. It is not a case of 'finders keepers'.

"Finders of wreck have 28 days to declare their finds to the receiver. This case highlights the importance of doing that and demonstrates what could happen to you if you don't.

"By reporting wreck material you are giving the rightful owner the opportunity to have their property returned and you may be adding important information to the historic record.

"Legitimate finders are likely to be entitled to a salvage award, but those who don't declare items are breaking the law and could find themselves facing hefty fines."

English Heritage assessed the importance of objects seized and has provided expert advice to investigators.

Mark Dunkley, the organisation’s maritime designation adviser, said: "The investigation has highlighted the need to tackle heritage crime, wherever it occurs, so that the remains of our past remain part of our future."

The pair appeared at West Hampshire Magistrates’ Court, in Southampton – because that is where the MCA is based – and are due to be sentenced on Wednesday, July 2.

The MCA is appealing for help in finding six bronze cannons still missing. They were built in 1807 by W & G and have the English East India Company logo (VEIC) on them.

Anyone with information about where they are is asked to phone 02380 329 474.