David has been living with Madonna, her film director husband Guy Ritchie and her two children since last October.

The High Court of Malawi originally appointed Mr Kilembe, who is director of Child Welfare Services, to travel to the UK to monitor how David was settling into his new family life. His testimony was expected to be crucial in the final ruling next year on whether the celebrity couple should be allowed to adopt the child permanently.

There was strong speculation that he might judge Madonna's superstar lifestyle and close media attention unsuitable for the youngster.

Last week Mr Kilembe claimed that social services in povertystricken Malawi did not have enough cash to pay for two visits planned to see David in Britain.

A five-day trip in May to Madonna's homes in London and Wiltshire had to be cancelled for lack of money, he said. A first visit was instead scheduled for later this month with a follow-up trip in December.

"We have been unable to travel because of logistical problems," Mr Kilembe said on Friday. "It requires some resources for me to travel."

But if Madonna did try to solve the problem by funding his visits, she risks being accused of hoping to secure a favourable report.

The Malawi minister's anger appears only to complicate her case. Justin Dzonzi, a human rights lawyer who led a 65-member rights group challenge to Madonna's adoption, also said the minister's decision could halt the adoption process.

"The minister cannot change what the court set by having another person to do the assessment. The court will not listen to anyone else apart from the one it appointed," he said. Dzonzi filed the case arguing that Malawi laws forbid international adoption and therefore the government broke its own laws by granting Madonna an interim adoption.

A spokesman for Madonna declined to comment.