On the house, just because. (Chris Ratcliffe/Bloomberg News)

People who don't eat regularly at popular lunch spot Pret A Manger probably don't realize one of the best perks of being a customer there: Employees are frequently giving away free food.

Clive Schlee, the chief executive of London-based Pret A Manger, let everyone in on the secret this week. Rather than institute the sort of customer rewards program where people sign up to earn points to get occasional free stuff, Schlee tells employees to give away a certain amount of food and drinks. In fact, he has made it a part of their job.

"We looked at loyalty cards but we didn't want to spend all that money building up some complicated Clubcard-style analysis," he told the London Evening Standard on Tuesday. "Instead the staff have to give away a certain number of hot drinks and food every week."

Pret A Manger estimates that 28 percent of customers in the United Kingdom have been gifted something at some point. It's unclear what the number is globally, but the company said it expects that it's a comparable rate.

The idea of rewarding longtime patrons with free stuff has been around for a while, but Pret A Manger's program is pretty unusual, especially these days.

"It's way more of a traditional approach than you see elsewhere," said Rajiv Lal, a professor at Harvard Business School who researches the retail sector. "When you went to a store that was owner-operated, people used to make you feel as though you were special, they used to remind you that they knew you were loyal with random acts of kindness. But you don't see that a lot anymore."

Today, reward programs have become established and mechanized systems, where people who buy, say, 10 cups of coffee, get the 11th one on the house. Points are tallied on punch cards or, increasingly, card systems that log purchases. Starbucks's program, in which customers earn points that can later be used to make purchases, is one of the better-known examples.

There are good reasons for the current state of loyalty programs. In part, the evolution is simply an adjustment to the scale of businesses today. It also helps companies harvest information on what you like to purchase.

"A huge part of the value of loyalty programs is actually just in the data," Lal said. "Companies use that data to figure out what you've bought, and then adjust to your preferences. Or they just sell it to someone else, often for a lot of money."

By forgoing a formal system, Pret A Manger is relinquishing the ability to collect valuable information about what and when people buy certain things, information that could translate into cash or a more prudent strategy. The company also runs the risk of relying on a system that doesn't necessarily reward people for loyalty.

But in breaking from the norm, Pret A Manger also looks special — more personal and less corporate.

"People might actually be more inclined to go back since they were given a present instead of a deal," Lal said. "It's a much more personal form of gratitude."

So how do you get in on the deal?

"Shops are given a budget, but there aren't any rules," a company spokesperson explained.

For those hoping to be a recipient of a free coffee, there isn't anything in particular that guarantees a gift. Schlee joked on Tuesday that it doesn't hurt if an employee has a crush on you. Frequenting a single store, so people learn your face, probably doesn't hurt either. Nor does letting someone know how impossibly bad your day has been.

"They usually choose their regulars and customers they think are in need of cheering up," a representative said.