Those taking part in trials by Ohio State University Medical Centre in the United States said that their headaches improved significantly after using the device at the first sign that a headache might be developing.

The researchers found that the magnetic pulse triggered an electric current in the neurons in the brain.

This stopped the initial "electrical storm" - the first phase of a migraine - from developing into a full-blown attack.

The results of a small trial involving 23 migraine patients were presented yesterday at the annual meeting of the American Headache Society in Los Angeles.

The researchers are now planning a much larger study with the device, made by Californian company Neuralieve.

The machine interrupts the phase of the migraine where electrical activity in the brain increases before developing into a full-blown attack.

During this period sufferers describe seeing showers of shooting stars, zigzagging lines and flashing lights.

They also experience loss of vision, weakness, tingling or confusion, typically followed by throbbing head pain, nausea and vomiting.

About one in eight people in the UK suffers from migraines, with twice as many women affected as men. A migraine attack can last for between four and 72 hours and sufferers experience an average of 13 attacks each year.

Researcher Yousef Mohammad said that the patients in their trial reported a significant fall in feelings of nausea, noise and light sensitivity after treatment with the TMS device.

Two hours after receiving the magnetic pulses, 69 per cent of the patients said they had either no pain or only mild discomfort.

This compared to 48 per cent in the control group who were not treated with the device.

"Perhaps the most significant effect of using the TMS device was on the two-hour symptom assessment, with 84 per cent of the episodes in patients using the TMS occurring without noise sensitivity.

"Work functioning also improved and there were no side-effects reported," Dr Mohammad said. "The device’s pulses are painless. The patients have felt a little pressure, but that’s all."

Wendy Thomas, chief executive of The Migraine Trust, welcomed the latest study. She said: "The research is interesting, although it is worth noting that the number of patients taking part in the study was small - just 23 patients were actually treated with the device.

"There is a clear need for further, larger studies to be able to assess whether or not this treatment should be added to the existing treatment protocols."

She added: "There are a number of existing, clinically proven treatments for migraines and we would strongly advise anyone with migraines to visit their GP to ensure that they are getting the best possible treatment available today."

Ann Turner, director of the Migraine Action Association, also welcomed the new trial and said larger studies were now needed.

"It is good that we are seeing a different approach to tackling migraines, rather than just saying to patients to take this pill or take that pill.

"A lot of people are worried about taking medication so if we can avoid that as much as possible it is very encouraging," she added.