Baroness Amos is to step down as the United Nations humanitarian chief after four years, it was announced, sparking political controversy over the UK's choice of candidate to succeed her in the key role.
UN secretary general Ban Ki-moon paid tribute to the "outstanding" efforts of the Labour former cabinet minister who has overseen a particularly difficult period in world affairs, notably pushing for more help for the civilian victims of the Syrian civil war.
The largely unexpected departure has left Mr Ban until the end of March to choose someone to take the high-profile post of under secretary general for humanitarian affairs and emergency relief coordinator, which has been held by a British representative since 2007.
But suggestions that Prime Minister David Cameron could put forward former cabinet minister Andrew Lansley for the position has sparked concern in some quarters over his lack of experience of humanitarian work.
Oxfam chief executive Mark Goldring told Channel 4 News it was " not the signal that we as the UK would want to be giving the wider world" and former UN deputy secretary general Mark Malloch Brown said it would represent an act of "political dumping".
Labour MP Grahame Morris has written to Mr Cameron suggesting the nomination would "send the message that Britain sees the UN as a convenient dumping ground for failed Tory politicians".
A UN spokesman insisted that there was no suggestion the role was reserved for an individual from any one member nation.
The prospect of a top international job for Mr Lansley was fuelled by his letter to the Prime Minister when he was removed as Commons leader in July's reshuffle in which he thanked Mr Cameron for supporting his desire to take a " challenging and important" international post.
The PM replied that Mr Lansley, his former boss in the Conservative Party research unit who oversaw highly-controversial NHS reforms as health secretary, had " much more to give in terms of public service, and I look forward to being able to support you in doing so in the months and years ahead".
In a statement to Channel 4 News, Mr Lansley's office said: "There will be a UN recruitment process and he would not wish to pre-empt that or take it for granted. The appointment is a matter for the Secretary-General." The Prime Minister's office refused to comment.
Announcing Baroness Amos's decision, Mr Ban said in a statement: "Ms. Amos has tirelessly advocated for people around the world affected by disaster and conflict.
"For her, people have always come first. She also worked closely with humanitarian workers who often risk their own lives to serve people most in need.
"Her extensive experience, leadership and work in partnership with principals from the humanitarian community, has helped find solutions for people who are facing the worst experiences in their lives."
Lord Malloch Brown, a crossbench peer who served as a Foreign Office minister in the last Labour government, was scathing of the possibility of Mr Lansley being put forward to replace her.
"This is one of the most difficult, important jobs in the world. There are millions of people in desperate situations from Ebola victims to victims of war in Syria who are highly dependent on the humanitarian activities of the UN," he told Channel 4.
"It's an act of great cynicism to allow someone who does not have background and qualification in this area to be put forward."
Mr Goldring said: "I think a party politician who doesn't have a track record of international and of humanitarian work starts in a difficult position, because first and foremost they will be seen as a party politician rather than a humanitarian leader.
"It's not the signal that we as the UK would want to be giving the wider world for how do we work together on solving really challenging international crises."
Baroness Amos had served as international development secretary.