Sandwich chain Pret a Manger served up record-high sales in 2015, on the back of strong growth in the US, while the ongoing trend for healthy eating boosted sales in the UK.

In the 12 months to the end of December, sales rose 13.9% year-on-year to £676.2m (€854.2m, $968.2m) with sales at branches that have been opened for over 12 months increasing 7.5% from the corresponding period in 2014. Meanwhile, earnings before interest, tax and other items increased 14.5% year-on-year to £84.3m.

Pret's vegetarian options performed particularly well, with the company's sales of a new beetroot, squash and feta salad reaching 17,000 weekly units, higher than sales of salmon and chicken options.

Clive Schlee, the group chief executive, revealed some 10,000 customers voted on social media on options for improving the chain's vegetarian range and the company has unveiled plans to turn its Soho branch in London into a veggie shop.

"Last year thousands of customers told us they were trying to eat less meat," he said. "This year we have challenged ourselves to increase our vegetarian options in all shops, as well as opening a veggie-only pop-up shop to learn more from our customers."

The growing popularity of avocado also boosted sales, as Pret sold 5m of them in salads and sandwiches over the course of last year, making it its fastest-growing single ingredient.

Pret added that its US business, which was first launched in 2001 and now has 65 branches, performed well as sales at established stores grew 13.8% year-on-year.

Meanwhile, the group, which opened 36 new worldwide branches last year taking its tally to 399, unveiled plans to continue to grow steadily in Britain after opening 23 new stores across the country in 2015. it began in the UK with one shop in London's Hampstead.