A hosiery industry veteran whose brainwave led to the invention of a thermal sock which has taken the UK by storm is poised to see his fortunes soar as the product prepares to break into the US market.

David Doughty came up with the idea of the Heat Holder, which is dubbed the ultimate thermal sock and has sold in its millions.

Mr Doughty, chief executive of Whetstone hosiery firm David James, was determined to create a better thermal sock after suffering cold feet while watching his teenage son play rugby.

Now Manchester-based Ruia Group, which owns David James, has clinched a deal to sell the revolutionary socks at an unnamed US retail chain, which has thousands of stores.

At the same time the company aims to double UK annual sales of Heat Holders to six million pairs and has begun selling online into Europe.

Mr Doughty, who has been in the hosiery industry for 40 years, said: "Heat Holders were invented on the playing fields of Uppingham School. My youngest son, Connor, was 13 in 2005 and I was standing watching him play rugby. It was January and it was freezing cold. My feet were frozen and I was wearing a pair of thermal socks bought from a high street store.

"On the Monday morning I rang my eldest son Shane (buying director at Ruia) in Manchester to see if we could come up with a sock which could keep your feet warm. We asked our suppliers to come up with some ideas."

An Indonesian supplier got in contact and said it would make a change to its machinery that made the socks in such a way that enabled them to trap more warmth.

Tests found Heat Holders, sold under the Ruia-owned Sock Shop brand, have a tog (thermal overall grade) rating of 2.34, compared to 0.89 for ordinary thermal socks.

Mr Doughty said retailers doubted at first whether there would be much demand.

The socks, which are made in Indonesia, are now sold by 40 retail groups across the UK, including Tesco, Debenhams, TK Maxx, House of Fraser, Sports Direct and Matalan. Matthew Hayes, managing director of Champions UK, of Costock, near Loughborough, is overseeing the global marketing of Heat Holders.

"It could easily be tens of millions of pairs a year that we sell," he said.

"The US market is seven times the size of UK and there is nothing similar out there."

"Heat Holders have been very successful," said Mr Doughty. "I have never made so much money in my life. My family has been in the sock industry for a long time. We now go back four generations in it. It has been quite gratifying, but I could not have done this without my son Shane."

Heat Holders has now expanded into thermal underwear, which is manufactured in Portugal.

Mr Doughty worked on the shopfloor for Leicester hosiery firms Byford and Pex during the 1970s before being made redundant. He then started up on his own, forming Mark Shane Hosiery in 1980. At its height in 1988, the company, based in Wigston, employed 250 people across three sites.

It was then hit hard by low-cost overseas competition. Mark Shane was wound up in the early 1990s. David James, in Bruce Way, off Cambridge Road, Whetstone, was founded in 1994.