A weigh-in at the Jubilee Sailing Trust Pumpkin Festival in Netley, near Southampton, found Mark Baggs's pumpkin weighed 1,520 pounds (689kg).
Festival organiser Sonja Davison said the monster specimen was 16lb (7.3kg) heavier than the previous UK record.
Specialist lifting equipment had to be used to move the giant pumpkins for the event at Royal Victoria Country Park, the BBC reported.
Baggs, 30, had dedicated most of his spare time to growing the pumpkin, which he cultivated from a specially- selected seed planted on April 13. He grew his prize pumpkin in a polytunnel.
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The record for the world's heaviest pumpkin was set on 15 October 2011 in Ontario, Canada.
The pumpkin, weighing 1,818lb and 5oz (824.86kg), was confirmed by Guinness World Records as the heaviest ever.
He once claimed the world record for the heaviest marrow, grown in 2005, weighing 136 pounds (62kg), the report said.
Baggs does not know what the organisers will do with the pumpkin, but agrees it would make a terrifying Halloween lantern.