British researchers say the level of caffeine in cappuccinos and espressos at popular chains varies.

While a single shot of espresso at the Caffe Nero chain would provide a coffee enthusiast with 45mg of caffeine, the same-sized drink at Pret contained 180mg, the consumer rights and research group Which? reported on Wednesday.

“How much caffeine is in your coffee depends on what type of coffee you buy and where you buy it from, our research reveals,” said Sheefali Loth, a researcher at Which?.

“It can be hard to tell as levels vary so much, even in seemingly identical coffees.”

Researchers looked at the caffeine content at five popular high-street outlets – Caffe Nero, Greggs, Pret, Starbucks and Costa – in their single-shot espresso, cappuccino, and filter/brewed coffees.

Pret’s espresso and filter coffee had the highest amount of caffeine, while Costa had the most in a cappuccino with 325mg – five times more than Starbucks. The Seattle-based chain had the lowest caffeine content across all three categories.

Caffeine is a stimulant found in coffee, tea, cocoa and more than 60 other products – and consumed by millions of people around the world daily.

Scientists say coffee has been shown to have beneficial health effects, including improving liver and heart conditions, but link consuming large amounts to stress, anxiety and insomnia.

Pregnant women and those nursing are advised to consume less.

Why the difference?

Loth said the reason why caffeine content differs is partly due to how much coffee is being added.

“Most coffee shop brews will have at least two shots of espresso in them, but some have more, meaning your caffeine intake can quickly add up,” she wrote.

The type of coffee beans or blend used also has an effect.

Expert Charles Love at Whittard of Chelsea, a British chain specialising in tea and coffee, told Which? that Arabica, which is used by most coffee chains, contained about “half the caffeine levels” of Robusta – another blend.

Roast levels also determine the caffeine content, as well as temperature, steeping time and quality of the grind, experts told Which?.