Madonna's controversial adoption of an African baby was under threat last night amid accusations that the child welfare expert overseeing it has become too close to the case.

Penstone Kilembe has been banned by the Malawian government from travelling to Britain to review the progress of 23-month-old David Banda, who has been in the care of the singer for nine months.

Last night Mr Kilembe said the development could result in the adoption being called off.

According to a newspaper report in Malawi, the Minister of Women and Child Development, Kate Kainja, accused him of obtaining an air ticket to London and money from Madonna herself without his government's approval. The minister refused to allow Mr Kilembe to travel to assess the case, accusing him of "personalising" the matter.

She suggested that by accepting funding from Madonna he had compromised his neutrality.

"We have already contacted Madonna that someone else and not Kilembe will come to assess her, because we feel Mr Kilembe personalised the whole issue when other people can go," the Minister told the Malawi News.

The revelation is likely to prove hugely embarrassing to the 48-yearold singer and could halt the adoption process altogether.

Last night Mr Kilembe confirmed that he had been banned from making the trip, but denied that he personally asked the American star for a plane ticket.

He claimed that the decision to exclude him from the final decision on whether or not Madonna is allowed to keep David may result in the child being sent back to Malawi.

"What this means is that the whole adoption process may crumble and David is sent back to his village," he said.