Vincent Woolsgrove reported finding five 17th-century cannons during the summer of 2007 but said just two came from the wreck of the warship London, which sank off Southend in Essex in 1665.
The other three, he claimed, he had found in international waters off the coast of Kent. The 48-year-old was awarded the title of the three Dutch cannons because the Maritime and Coastguard Agency was unable to prove they were property of the Crown.
Woolsgrove then sold them to a US collector for more than £50,000. But a two-year investigation by the MCA established that the cannons were issued to Dutch ships in the 1650s and captured by the English in battle.
The MCA, together with Kent and Essex Police and Historic England (formerly English Heritage) found that the three Dutch cannons had been issued to the Dutch vessels Groote Liefde and St Mattheus.
They attacked the English fleet during the first Anglo-Dutch War in 1653 but the vessels were captured by the English and the cannons taken as prizes.