There's nothing like a nice cuppa (to induce stress, sleepless nights and anxiety)

For 300 years it has refreshed a nation, quenching the thirst of builders and politicians alike. But tea, Britain's favourite stimulant, may soon find itself in hot water.

Academics in Bristol have launched the country's biggest investigation of the cuppa to see if our national drink is leaving us prone to high levels of sleeplessness, anxiety and stress. Despite its mild reputation, a strong cup of tea contains as much caffeine as a cup of instant coffee, according to the team conducting the government-funded project.

It is led by Professor Peter Rogers, a psychologist at Bristol University who specialises in the mental effects of caffeine. He said: "We've got questions about sleep patterns, and mood and stress patterns. We will be asking about the relationship between caffeine consumption and mood, stress and sleep - these are rather important.

"We will also be asking people what the immediate effects of drinking tea and coffee are - does it make me feel relaxed, make me tense or give me a headache?"

To the irritation of the tea and coffee industries, Professor Rogers says that caffeine is addictive. "The general perception is that tea and coffee have different effects on people but in fact, the way people in the UK drink tea, a strong cup of tea has about the same caffeine as a cup of instant coffee," he said. 5,000 people are being recruited to take part in the experiment.

Caffeine is said to be the most widely consumed drug in the world, and in Britain we get plenty of it, drinking an average of 165 million cups of tea every day, or 62 billion cups a year, and 75 million cups of coffee a day.

The three-year project, funded by the Biotechnology and Biological Sciences Research Council, will study the effects of all popular drinks that contain caffeine: coffee, soft drinks like Coca-Cola and Pepsi, and energy drinks like Red Bull, which has the same caffeine content as a cup of filter coffee.

The Dietary Caffeine and Health Study will try to find out whether there are different types of tea and coffee drinker. They will range from typical consumers who get mild, positive affects from caffeine; those who believe it's bad for them and rarely drink them; those who get anxiety attacks; and caffeine "addicts". It will also investigate the theory that some people are "natural" caffeine users, while others are genetically predisposed to becoming anxious or panicky after taking tea or coffee.

The research programme has put the associations representing the tea and coffee industries on their guard, although they acknowledge Professor Rogers's credentials. They are critical of his belief that caffeine is addictive, and highlight the many studies that have revealed the health-giving properties of tea in particular.

Bill Gorman, director of the Tea Council, said studies had suggested the flavinoids in tea are effective in preventing some cancers, and helped clean the blood of toxins. Both the World Health Organisation and Food Standards Agency had cleared tea as safe during pregnancy - despite fears that caffeine can affect blood pressure.

Roger Cook, director of the Coffee Science Information Centre and spokesman for the British Coffee Association, said sensible coffee drinking could have a positive effect. "There are two sides to every argument. It has been shown that caffeine can have beneficial effects at certain times of the day, particularly with alertness and performance," he said.

UP FOR THE CUP: DEFENDERS OF THE GREAT BRITISH DRINK

Tony Benn has a fondness for rubbing tobacco, has never drunk alcohol, and claims to drink a pint of tea every hour. "Once on a train, I worked out I have drunk enough tea to float the QE2."

Samuel Johnson, the 18th-century man of letters,drank 40 cups a day: "Tea's proper use is to amuse the idle, and relax the studious, and dilute the full meals of those who cannot use exercise, and will not use abstinence."

Boy George entered tea-drinking mythology when he told Terry Wogan he would rather have a cup of tea than sex

Kate Moss drinks up to 12 cups a day and promotes the drink for the Tea Council. Moss lists tealeaf-reading as one of her hobbies