Douglas Smith, 42, spent more than two months carefully growing the giant tomato, which weighs a whopping 6.6 lbs. and is actually six regular beefsteak tomatoes fused into one.
The huge fruit, which had to be suspended using a pair of tights so it did not fall off the stem, weighed in at a whopping 6.85 lbs., and measured 27.5 inches in circumference.
It was grown from a seed from a variety known as Big Zac.
Smith's monster has edged ahead of the previous U.K. record-holder, Peter Glazebrook, whose record-winning tomato last year weighed 6.4 lbs.
"This has been an ambition of mine for a couple of years, now," Smith, from Stanstead Abbotts, England, said. "Giant tomatoes have been my main focus in terms of competitive vegetable growing."
He's made two previous attempts, but he was bested by Peter Glazebook.
"And my attempts have been just shy of his each time, he said. "But this time, I've finally edged it."
Product manager Smith hit the headlines last month after growing a giant sunflower as tall as his house, which towered at an impressive 20 feet tall.
Now, he has shared the secret to growing his "amazing" giant tomato, which is due to be sent to butchers' shop Churchgate Sausages in Harlow, Essex, to be made into tomato and basil sausages.
"What you want to try and cultivate is a fused flower, which is where the individual tomato plants fuse altogether in a row, Smith said. "This particular tomato is made up six tomato plants all fused together."
Fused flowers tend to be a natural mutation, but with competition seeds specially selected there was a slightly higher chance of this occurring.
Fused flowers tend to occur more often on the first truss of tomatoes and when is a spell of warm days and by cool nights, like at the end of summer into autumn.
"It's also important to cut back any other flowers on the plant to maximize all the growth into the one 'megashoot,'" he said.
Smith got the seeds for his giant tomato from U.S. tomato grower Larry Hill, from Minnesota,who yielded the seeds from his own, 7.65-pound tomato plant.
Smith watered his tomato plant at least once every day for more two months, using water with a bit of liquid seaweed mix.
And he also gave the plant a weekly compost tea feed consisting of a bucket of compost blended down, to help improve the soil life.
"A lot of it is to do with the genetics of the seed, and proper soil testing in a laboratory, to make sure the soil conditions are right for the tomato to grow, he said. "It's important to keep the temperature in the greenhouse steady."
Temperature matters. At the first stage of growth, the plants need about 20 degrees C (68 degrees Fahrenheit) throughout the day and through the night.
"Then as it gets a bit bigger, you can let the temperature drop a bit at night but not below about 18 degrees C (64 degrees F)," he said.
It is important to keep the tomato shaded by covering it with something like a dishcloth because it keeps the skin supple so it can grow.
"I actually had to hang it in a sling towards the end, made out of a pair of pantyhose I had bought to provide it with support and keep it falling off the stem" he said.
And Smith said that the "amazing" thing about his tomato was that it was grown in a pot, rather than in the ground.
He said: "I don't like growing things in pots - I prefer to grow things in the ground.
"But one of the competition categories was the biggest plant grown in a small pot.
"This tomato was grown in an 18.9-litre pot - which makes its size even more amazing."
Smith will now keep the seeds from his huge tomato to continue growing more of the fruit.