The UK’s sunny spring weather has provided “perfect” conditions to produce strawberries so big you “cannot fit them in your mouth”, UK growers have said.

With nearly 20 years’ experience, Bartosz Pinkosz, the operations director at the Summer Berry Company, has “never seen anything like it”. The strawberries being harvested this month by the leading grower are whoppers thanks to the combination of lots of sunshine and cool nights.

“We had the darkest January and February since the 70s but then the brightest March and April since 1910,” he said. “From March onwards it was really kind of perfect for tunnel strawberries. The berries are between 10% and 20% larger.”

Berries grown at the company’s farm in Colworth, West Sussex, are sold by all the big retailers and, while sizes vary, Pinkosz said its strawberry plants are yielding “giant” 50g berries you “cannot fit in your mouth”. However, the average is a more modest 30g.

Nick Marston, the chair of the industry body British Berry Growers, confirmed the (fruit) salad days ahead for strawberry lovers. “We’re seeing very good size, shape, appearance, and most of all, really great flavour and sugar content, which is what consumers want when they buy British strawberries,” he said.

He added: “I’m always a little cautious of saying strawberries are 20% bigger because there’s an average involved and some crops will be slightly smaller than others. But I think it would be fair to say the very nice sunshine, the cool overnight temperatures, are ideal for fruit development.”

The blockbuster berries in the Summer Berry Company’s tunnels were “tastier and firmer”, Pinkosz said, because the cool nights enabled the fruit to ripen slowly. “The slower the development of the fruits, the more time to expand the cells and create the bigger berry. What we are now seeing is something I have never seen in 19 years, which is consistently larger berries.

“It has been a perfect start to the strawberry season for us ... I have genuinely never seen a harvest produce such large berries consistently. Some are supersized – growing to the size of plums or even kiwi fruits.”

The sunny, very dry spring, with the warmest start to May on record, delivered a glut of early strawberries, aubergines and tomatoes at the start of May. But as the dry conditions persist there are fears that Britain is heading for a drought this summer.

Marston said the spectre of water shortages would be a cause of concern, particularly for growers in the south-east of England. However, he said berries were grown using drip irrigation so water was used very sparingly.

As Wimbledon approaches next month, tennis fans could be treated to juicy, supersize strawberries for a second year in a row after wet and dark conditions slowed growing times last year.