Having already persuaded Asda and Tesco to sell Uncle Joe's Mintballs in North West stores, William Santus and Co is now finalising an agreement with Sainsbury's.

It is a further sign the sweets are gradually working their way into the mainstream and the new contract leaves the Dorning Street firm with only the worry of how it will keep up with production.

The firm, more than 100 years old, may have to take on more staff to cope.

The mintballs are set to go on sale in more than 30 Sainsbury stores across the region and are a further indication the chain is now buying into the "locally sourced produce" ethic that some of its rivals have been championing for several years.

William Santus co-director, John Winnard, said: "The supermarkets are taking notice of what the public wants and are also ever more mindful of their carbon footprint, so the more produce they can source locally, the better.

"We are ecstatic with the Sainsbury deal. The main thing is it will be a struggle to keep up with production, especially in winter when sales increase. This could create more jobs in the long run."

Mr Winnard said one of the biggest current challenges was retaining staff.

He said: "In years gone by you would take someone on and it would be their job for life. These days you train someone up and then they decide to go off and do something different."