The device uses electric pulses to increase brain activity, and medical trials suggest the equipment could work well.

It is now being tested on NHS patients, but anyone hoping to purchase one privately could have to pay up to £399.

Swedish company Flow Neuroscience created the device. It said the headset stimulates certain areas of the brain that are not as active in depressed people, and the electric currents are gentle and "non-invasive".

The firm claims 88% of depressed patients who trialled the device were in remission after six weeks - with 74% remaining in remission six months on.

Annie Lovatt, 24, has been using the headset for three years, having started off by wearing it for 30 minute intervals five times a week.

"I was really unwell, really unhappy," she said. "This kind of felt like a last resort, and it was like if this doesn't work, I don't know what will. I was really lucky that it did."

'A switch flicked'

Ms Lovatt noticed a huge change to her mental health just three weeks into wearing the device.

"It was like a switch flicked," she said. "And it was just so much better.

"Like one morning, I just remember waking up and noticing that I just felt better. Like, I just felt more able to get out of bed and get on with life."

Ms Lovatt had tried anti-depressants but didn't feel they were effective, and struggled to sleep while taking them.

Her mental health deteriorated so badly she was unable to leave the house or even get dressed in the morning.

"I know for a lot of people it's a bit more gradual. But yeah, for me, it was a really dramatic reduction," she said.

Ms Lovatt now wears the headset twice a week while she watches TV and crochets. She also has therapy.

However, Annie found she experienced relapses when she wasn't using the Flow device consistently.

Long-term questions

The doctor leading the NHS trial has said some patients had come off antidepressants and were now just using the headset to manage their symptoms.

Dr Azhar Zafar would now like to see the devices rolled out across the health service.

"If you look at the overall benefits it can give to our patients by reducing the numbers attending GP surgeries, seeing healthcare professionals, I think it will give a benefit," he said.

"Overall, the cost will not matter if it's giving so much benefit to our patients."

But the cost is likely to be a factor in this product becoming more widely available on the NHS - and there are also concerns about how the treatment works long-term.

GP Dr Anita Raja said: "The main question so far that has arisen with regard to this device: it works so long as you are using it, but when you stop using it what happens?

"Is the person cured of depression? Does the person relapse?"

The National Institute for Health and Care Excellence says on its website: "There is not much good evidence about how well transcranial direct current stimulation (tDCS) for depression works, particularly how many treatments are needed and how long the effects last. But there are no major safety concerns."