If the advertisement is a way of procuring profit and money for someone then that is obviously moving away from the needs of the child

Gill Howarth, Overseas Adoption Helpline

But in all but three American states, adoptions are allowed to be conducted privately, with the biological parents choosing who should adopt their child.

With no restriction on adoption from overseas in UK, many British people look to the US to adopt a child and use the internet to find one.

To prevent a trade in "black-market babies", almost every state bans agencies and individuals from taking fees for finding or placing a child.

However, in most cases a sum is usually paid to the natural mother for medical expenses.

In the case of celebrity adoptions, including Sharon Stone, Calista Flockhart and Nicole Kidman, the sum has been substantial.

The internet has allowed the trade in private adoptions to become big business.

Internet adoption began in America in late 1994, when a housewife in Waco, Texas, created a computerised photo listing of children up for adoption.

Legal fight

There are now hundreds of agencies across the world offering their services and websites display hundreds of thousands of children each month.

While private adoptions work out for many, British adoption agencies say the Kilshaw's case highlights how the system could throw up problems.

They are reported to have paid �8,200 for six-month-old twin girls.

But a US family claim they had already paid �4,000 to an internet adoption broker for the girls.

The couple from north Wales now face a legal fight to keep the babies.

'Highest bidder'

The adoption broker who organised the deal and the children's natural mother have both disappeared.

While British adoption agencies do not object to advertising for prospective parents on a website, they say the needs of the child must be put first in all private adoptions - by everyone involved.

Gill Howarth of the Overseas Adoption Helpline said UK agencies have been advertising for families to adopt for years.

"It is not the advertising that is the issue, " she said.

"Many adoption agencies in the UK have for 20 years or more used different media to raise awareness about the need for adoptive families. That is the reason why the internet is used.

Children have a right to live in secure, loving families. Adults do not have an automatic right to adopt

British Agencies for Adoption and Fostering

"But the child must be at the centre of all adoption services and plans. If the advertisement is a way of procuring profit and money for someone then that is obviously moving away from the needs of the child."

British Agencies for Adoption and Fostering (BAAF) said the Kilshaw's case demonstrates why private adoption is illegal in the UK.

A spokesman said: "Children have a right to live in secure, loving families. Adults do not have an automatic right to adopt.

"It is totally unacceptable to the BAAF that children are sold to the highest bidder.

"It is vital that those who wish to adopt from overseas take proper advice before they enter such a minefield."

It added that while advertising on the internet was a legitimate way of attracting prospective parents, they all had to be properly vetted before they adopted a child.