After 18 years of trying for a child, and thousands of pounds spent on unsuccessful fertility treatment, Wendy and Brian Duncan feared their time was running out. They flew to Mumbai, formerly Bombay, and came back pregnant with an Indian baby.

The Duncans had joined the growing stream of Britons seeking fertility help abroad because they could not afford it in the UK. Their beautiful, dark-eyed daughter Freya is now 10 months old.

Mumbai doctors treating 39-year-old Wendy Duncan were not confident embryos from her own eggs would develop, so she asked them to implant four donated embryos along with two of her own. 'The doctor had to think about it because he had only Indian embryos for adoption, no white ones, and he had not done that before for a white couple - we sat up all night talking, hoping he'd say "Yes," and he did,' she said. 'We laid bets on whether it would be ginger like me or not while I was pregnant. It was only when the midwife told me that she could see lots of black hair we knew it was an Indian embryo that had taken. I had the feeling all along it would be. I don't have words to describe how happy we are.'

Websites advertising Indian clinics have enticed more and more couples to take the radical step of consulting doctors thousands of miles away, where treatment is cheaper, quicker and less tightly governed than in the UK. Regulators in Britain have expressed concern at the ethical and clinical risks involved, and warn couples to think twice.

Going to India was traumatic for the Duncans, who had never visited Asia. Friends told them they were 'insane' to make the trip to Mumbai and their doctors strongly advised against it. 'When we got off the plane we almost turned back. The airport was full of men with guns, and the pavements were covered with people living in tents and cooking on open stoves on the streets,' Mrs Duncan said. 'It was filthy and there was such poverty, beggars with tiny babies. It was terrifying - not for the faint-hearted.'

The clinic they chose was in a shabby district. Patients ride to a fifth floor apartment in a shuddering lift. Inside, the atmosphere is welcoming. Hundreds of pictures of newborns cover the walls, and stuffed toy animals hugging baby animals are arranged on every available surface.

Aniruddha Malpani and his wife Anjali say their clinic has served growing numbers of foreigners since they created a website in 2000. 'About 15 per cent of our patients are foreigners with no family connection with India. In 2002 we saw about five patients in the entire year, in 2004 we treated 15, and now we treat at least one foreign couple a week,' Dr Malpani said. 'For our patients from the UK there is major grief as far as the NHS is concerned. People are so unhappy with the long waiting lists - and delays of three to six months before they can see a specialist.'

As Mrs Duncan had a daughter, now 19, with a previous partner and was overweight, she was barred from IVF treatment on the NHS. The couple borrowed £8,000 for one private treatment, which failed. They sold their shop and looked at heading abroad. India appealed because it had English-speaking doctors. The total cost, including flights and hotel stay for a month, was £4,000. Mr Duncan said. 'It wasn't just that India was cheaper. People were prepared to spend time with us; we felt like human beings.'

The couple received intense treatment now banned on safety grounds in the UK, where doctors will implant only one or two embryos; Mrs Duncan received six.

Their GP in the UK was furious, pointing out the risks to the mother and the potential cost to the NHS of treating a woman bearing sextuplets. Other health professionals were equally disapproving.

'Their attitude was that people like us were going abroad to get treatment, and then coming back to dump any problems on the NHS,' Mr Duncan said. 'Our attitude was that if the NHS had been able to help us in the first place, we wouldn't have gone abroad.'

Friends and family gave their full support. 'My eldest daughter is mixed race and Brian has been her dad since she was six months old,' said Mrs Duncan. 'So we both know what Freya might expect.'

In another Mumbai clinic, Sunita, 46, a newsagent from Leicester, was seeking treatment she is deemed too old for in England. 'Coming here has been very stressful, but I'm at a time of life where I feel like if I don't try this now, it's never going to happen for me,' she said.

Firuza Parikh, her doctor, does not usually treat patients over 43, but made an exception despite the slim chances of success. 'Patients get so frustrated by the wait in the NHS. They think that they will be too old by the time they finally get treated, if they are eligible according to the postcode lottery,' Dr Parikh said.

At his Assisted Conception Unit, Hrishikeh Pai said his foreign clientele was growing so fast he planned to open a second clinic in Goa, so Europeans could take a beach holiday during treatment.

Medical tourism of all kinds is forecast to become a $2.3bn business in India by 2012, with predictions it will be the next major driver of the economy after the IT industry.