Female infanticide is highest in some of India's wealthiest districts

The Oxford University study suggests 1,500 girls are "missing" from the birth statistics in England and Wales from 1990 to 2005.

It shows the proportion of boys compared with girls born to Indian-born mothers has increased since the 1970s.

Dr Sylvie Dubuc said this could be due to "sex selective abortion".

Dr Dubuc, who studied birth rates of different ethnic groups in England and Wales, found that in the 1970s 103 boys were born for every 100 girls.

Between 2000 and 2005, the proportion of boys over girls had increased abnormally to 114 boys for every 100 girls, she said.

Unfortunately it was another girl - my husband and I thought the burden would probably be too much Unnamed British woman Britain's unwanted girls

Figures showed 26,662 babies were born to Indian-born women in England and Wales from 1990 to 2005, excluding the first or second child.

"According to my calculation around 1,500 girls are missing... it's significant compared to the total number of births," Dr Dubuc said.

She said the most probable explanation seemed to be sex selective abortion by a minority of mothers born in India.

Reconstruction: 'Meena' went to India to abort her daughter Full interview

One British woman, who spoke to the BBC anonymously, said she had an abortion after a doctor in India found she was to have a fourth daughter.

"Unfortunately it was another girl. My husband and I thought the burden would probably be too much and the pressure when I got back home. So we decided to terminate," she said.

In Indian culture, the preference for boys over girls is well known.

Getting rid of baby girls is a practice that is so widespread in some parts of India that it has skewed dramatically the ratio of males to females.

Female foeticide, as it is known, has been illegal in India since the early 1980s.

It is also illegal to offer scans to find out the sex of a baby - but the law is regularly flouted.

Undercover filming

To see how difficult it is to find a doctor willing to carry out the service, the BBC sent a British couple to one of Delhi's top gynaecologists, Dr Mangala Telang - a doctor recommended by the British High Commission.

Dr Telang, an IVF treatment specialist, has practised in some of Delhi's top hospitals and has actually campaigned against female foeticide calling it an "evil" crime.

The BBC had heard that her clinic would offer ultrasound scans to determine the sex of a baby - even though a sign in the waiting room clearly said it was illegal.

FACTS AND FIGURES Female infanticide occurs in 80% of Indian states Worst-affected states include wealthiest areas 927 girls born for every 1,000 boys Infant mortality rate: 60/1,000 Source: Unicef

Secret filming shows that within minutes Dr Telang agreed to perform the scan. She warns the couple not to tell anyone about what they were doing as it is illegal.

The couple also ask whether, if the unborn child is a girl and they decide to abort the baby, she could recommend someone to carry out a termination.

Dr Telang says: "Yes, I can recommend someone."

In the ultrasound room, another doctor tells the couple the "good" news that it is a boy. Both doctors had broken several laws.

When the BBC told the doctors about the evidence, they denied doing anything wrong.

Dr Telang said she was not in the room when the scan was carried out. But she is clearly seen in the room congratulating the couple.

Cultural pressures

An estimated seven million girls have gone missing from India's population over the last 25 years.

Some of them will have been killed after they were born, or allowed to die within their first few days. But most of them will have been aborted.

Selective abortion is happening all over India as ultrasound machines - which carry out the scan - have become cheaper, but it has always been worst in Punjab and Gujarat.

It is impossible to say how many British women are travelling to India for terminations.

But the UK has a substantial community with strong links to, and often the same pressures as, families in India.

SEX RATIO OF BIRTHS TO INDIAN-BORN WOMEN IN ENGLAND AND WALES, 1969-2005

Birth of first or second child is excluded from these figures