The NHS spends £30million a year on insomnia treatments but till now it has been unclear how widespread the problem is because many people do not go to their GP for help.

Many people only suffer insomnia for a few weeks. Often when their stress problem goes away, so does their sleep crisis.

But for people with chronic insomnia, sleeplessness can go on for months and even years, causing huge distress, personal problems and illness.

The survey findings came as a separate study suggested a link between insomnia and high blood pressure.

Research into 1,700 volunteers by Penn State College of Medicine, in Pennsylvania, showed that those who slept fewer than five hours a night were five times more likely to have high blood pressure than the average person.

Those who slept well for more that six hours were not at raised risk of high blood pressure. Dr James Walsh, of St Luke’s hospital, in St Louis, Missouri, said that the Stanford university study showed that waking at night was almost as important as not being able to get to sleep.

“This is the first really good data we have showing the importance of nocturnal awakening in insomnia,” he said. “It shows a strong overlap between the awakening and other sleep problems and it suggests that nocturnal awakening is a very under-appreciated aspect of insomnia.”