By Alex Stevenson
Downing Street insisted Gordon Brown's "government of all the talents" has been a success, despite the resignation of three 'goats' in recent weeks.
Health minister Ara Darzi became the latest to stand down from the government to spend more time with his research last night.
He follows Foreign Office minister Mark Malloch-Brown and the man behind the Digital Britain white paper, Stephen Carter.
"The prime does think bringing people in from outside politics has been a success," the prime minister's spokesman said.
"These people are not professional politicians. it's no surprise they would want to move on after a period of time."
No 10 pointed to existing 'goats' within the government as evidence that the experiment is not completely dead - City minister Paul Myners, Mervyn Davies under Peter Mandelson and security minister Alan West.
"In general terms, the prime minister does think that these people have made an excellent contribution to the government and to public life, and so yes, he thinks it's worked," he said.
Lord Darzi, brought into the Department of Health as part of Gordon Brown's 'government of all the talents', made his biggest impact as the author of a major review of NHS services.
Yesterday it emerged he planned to resign his post at the start of the long parliamentary recess, which begins when the House rises next Tuesday.
"I believe that it took great courage to appoint a frontline doctor to undertake a fundamental review of the future direction of the NHS," Lord Darzi wrote to the prime minister.
"I am deeply grateful to you for having given me the privilege of serving in your government, the freedom to make tough but important decisions, and the support to make change happen."
But he added: "The time has now come for me to return to care for my patients, lead my academic department, and continue my research on a full time basis."
Lord Darzi will continue as an adviser to the government on its life sciences strategy.
He will also chair a new forum called NHS Global, No 10 said, which will "support the promotion of the NHS and UK healthcare and life-sciences industry internationally".
Responding to the resignation, Mr Brown told Lord Darzi he had made an "outstanding contribution" and described his NHS review as having "created a movement for change".
It is not clear whether he and the other goats will be replaced by more goats.