Britain's hot and dry summer has put this year's World Conker Championships in jeopardy with a series of heatwaves leading to smaller than normal conkers, organisers say.

The event began in 1965, raising thousands of pounds for charity, and since 2013 conkerers from around the world have descended on the Shuckburgh Arms pub in the Northamptonshire village of Southwick.

This year, however, Britain's horse chestnut trees, on which grow the shiny inedible nuts used to play conkers for generations, are not delivering their usual crop.

"It's been a worrying time, a really worrying time. Because we want the big, good, fresh conkers because they're the best for the championships," organiser Charles Whalley said.

"We hope that in a couple of weeks' time we'll be able to go around and collect the final conkers we'll actually use."

The game of Conkers involves inserting a string in a hole pierced through the nut before entering battle. Contests involve players taking turns to strike each other's nut with their own conker until one shatters.

This year's event is scheduled for October 10 and organisers are still optimistic it will go ahead as planned.

Duels are umpired to prevent foul play.

Last year's men's competition proved controversial after the winner, 82-year-old David Jakins, was accused of using a steel conker. He was subsequently exonerated.

"We are gentlemen at the World Conker Championships and we don't cheat," Jakins, known as King Conker, said after being cleared.

"I admit I had the steel conker in my pocket, but I didn't play with it. I show it to people as a joke, but I won't be bringing it again."