The findings offer a new area of innovation for sports drink manufacturers, which have largely concentrated on carbohydrates until now. But they may also add fuel to the controversial debate about the use of caffeine in sport.

The natural stimulant was removed from the World Anti Doping Agency's (WADA) list of banned substances in January 2004 but it continues to monitor its use.

Admissions last month by several Australian athletes, including rugby captain George Gregan from the Wallabies, that they were taking caffeine tablets to boost performance suggest that there is increasing use of the substance in sport.

Under WADA's World Anti-Doping Code, a substance is banned if it meets two of three different criteria, including performance enhancement and damage to an athlete's health.

However the new research does not prove that the ingredient is performance-enhancing, say the researchers. They believe there is potential for a new type of sports drink.

The team asked eight endurance road cyclists to perform three slots of two-hour exercise sessions, cycling at 55 per cent of their maximum power output.

During the trial, the cyclists took one of three different sports drinks - glucose, glucose with caffeine, and plain water - especially mixed to taste the same. Samples of blood and expired air were taken every 15 minutes, in order to measure the absorption rate of carbohydrate.

The sports drink containing 5 milligrams of caffeine per kilogram of body weight vastly outperformed the other two drinks, according to the researchers.

Dr Asker Jeukendrup, director of the university’s Human Performance Laboratory and sports nutrition expert, said: "It is very difficult to regulate the intake of caffeine in an athlete's diet, as it is present in such a wide range of products like chocolate, nuts, flavourings and drugs, as well as coffee and cola."

"As long as caffeine remains off the banned list, I believe there is a case for a new generation of sports drinks that utilises caffeine for its positive affects on delivering carbohydrates."

Further research by the Birmingham scientists will investigate the levels of caffeine required to initiate a positive affect on carbohydrate delivery, and measure the actual increase in physical performance that caffeine containing sport drinks bring on.

WADA meets in September each year to review the list of banned substances, prior to enforcement the following year.