A few years ago, I was walking down the street when I encountered Julian Metcalfe, one of the founders of the Pret a Manger sandwich chain, and a man I have met socially a few times.

He proudly brandished a copy of the newspaper I was working for. "I'm sorry, Julian," I said. "If only I was carrying a rocket and crayfish sandwich!" Pret is one of modern Britain's success stories, and the news yesterday that they are creating 550 more jobs in the UK at a time when many businesses are going in the opposite direction says much about the durability and sustainability of Julian Metcalfe's original vision (not to mention the peculiarly British passion for the simple snack named after the fourth Earl of Sandwich).

Metcalfe is a poster boy for the new breed of British entrepreneur, having launched his idea on the British public in 1986, a good year for new ideas that have stood the test of time. (The Independent was also born in 1986.) The concept was simple: at the time, Britain was not the gastronomic paradise that it is these days, and Metcalfe - together with college friend Sinclair Beecham - wanted to create an outlet selling fast food they themselves would find appetising.

It sounds bizarre now, when there are posh sandwich shops and takeaway options of every ethnicity populating the nation's high streets, but, in 1986, the idea of a shop selling sandwiches using only well-sourced natural ingredients and avoiding additives and preservatives sparked a revolution in the British way of eating. Sandwiches with avocado in them? Or houmous? We'd never seen such a thing. Baguette? We only encountered them on holiday.

Added to which, Pret adopted a very modern corporate philosophy: even the lowest-ranking staff were made to feel part of the company's success. They get a silver star made by Tiffany for exceptional performance - and the final say on new recruits is given to their prospective workmates.

For all this - and notwithstanding Pret's well-publicised practice of delivering leftover sandwiches to the homeless - the company has had its share of criticism. In 2001, a chunk of its equity was sold to McDonalds, whose culinary principles, ethics and working practices would seem to be antithetical to Pret's own, and Metcalfe says now that "it was a PR mistake. I hoped we we'd gain a greater understanding of training, discipline and opening in foreign countries, but we didn't learn that many lessons." McDonalds sold out in 2008.

More recently, the Mayor of London criticised Pret for employing too many non-UK nationals, but yesterday's announcement of expansion included a rebuttal from the company, saying that staff in the stores reflected the ethnic breakdown of the population of the particular area, and as 85 per cent of Pret's trade is in London, it is hardly surprising that they have a multi-ethnic staff.

Nevertheless, Pret is a very British institution, built on the fact that, while Italy gave the world pasta, Germany gave us sauerkraut and France gave us the filet de loup de mer et langoustines grillées, purée de pommes de terre fumée, and sauce a l'anis etoilée, Britain's contribution to global gastronomy was two slices of bread with something in between them. Sounds like a brilliant recipe for a business to me.

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