The UK is showing a “lack of coherence” in its leadership of vital UN climate crisis talks this year and giving the damaging impression that the talks are not a high priority, one of the world’s leading voices on the climate crisis has said.

Mary Robinson, a former UN climate envoy and Ireland’s first female president, also said the perception that major British politicians, including the ex-prime minister David Cameron and former foreign secretary William Hague, were unwilling to take on the role of leading the COP 26 summit was damaging.

“It is not helpful that we are getting the impression that in the UK no one wants the job. I mean, come on! The UK asked for this, they pitched for this responsibility, they must carry it forward.”

“This needs to be an overarching priority, that needs to come across. I do not see a coherent drive for [the summit] in the UK.

“The UK’s handling of COP 26 has not become coherent enough for the UN even to be able to support them,” she added.

Robinson, the former UN high commissioner for human rights who chairs the Elders group of former world statespeople, served twice as a UN climate envoy and campaigns for climate justice.

Her exasperation reflects a growing disquiet among some leading international experts over the UK government’s leadership of the vital COP 26 summit, which remains without a figurehead after a tumultuous week.

Facebook Twitter Pinterest Claire O’Neill has been critical of Boris Johnson since her sacking. Photograph: Daniel Leal-Olivas/AFP via Getty Images

Last Friday, the former energy minister Claire O’Neill was abruptly sacked as president of the negotiations, the key role alongside the UN in bringing countries together to agree tougher limits on greenhouse gases. Since then, O’Neill has unleashed vitriolic attacks on Boris Johnson, alleging a lack of interest in the climate crisis, while Johnson’s failure to set out a clear vision of how the UK will get a deal at COP 26 has also been criticised.

“It’s a huge pity this is happening,” said Yvo de Boer, the UN’s top climate official from 2006-2010, who began the push for climate action that resulted in the 2015 Paris agreement. “The president of the COP really needs to be the force for stability in this process. You need someone in place who is reaching out to key countries to smooth this process.”

The sacking of O’Neill reminded him of “a very bad time in my life”, he said, when during the Copenhagen COP in 2009 the Danish prime minister removed the serving COP president, Denmark’s environment minister Connie Hedegaard, and installed himself to lead the process. That was one of the factors that doomed the Copenhagen summit to an acrimonious and chaotic end.

In this case, the sacking has happened sooner – meaning “this is not irreparable”, said de Boer. “But if it goes on, I think it will be damaging.”

Johnson must also do more to show the UK’s leadership in cutting emissions, beyond the promise to reach net zero by 2050, he said. “It’s very important that the UK has domestic policies in place that allow them to inspire confidence in other countries,” said de Boer.

One long-time observer of COPs, who asked not to be named, said Johnson’s handling of the launch, at which he failed to set out clear stepping stones to a successful outcome for COP 26 or domestic policies to reduce emissions, had hurt his standing among world leaders on the issue. “There was nothing there, it was a mess,” they said. “It made me angry.”

However, there is still strong support for the UK’s COP 26 presidency and a willingness among many leading figures to assist Johnson and the government in building the coalition of countries needed. At COP 26, governments are being asked to come forward with tougher targets to cut greenhouse gas emissions, as the current targets are too weak to meet the goal of the Paris agreement in limiting global heating to 2C above pre-industrial levels.

“COP 26 needs to send a signal, to give guidance to governments and businesses [to encourage them to cut carbon],” said Fatih Birol, executive director of the International Energy Agency, and one of the most respected voices globally on climate issues. “I am sure that the UK will be a good manager of the COP.”

He said the UK had the diplomatic heft to forge the coalition of countries needed, even without a COP president currently. “I know the UK civil servants [working on climate], they have top notch climate experts, some of the best in the world. I have full confidence in them.”

But he called for the government to show more urgency. “Building a team needs to happen immediately, and putting out a clear vision for COP 26. You need leadership, the engagement of all the key parties, including developing countries, and all other stakeholders [including business and civil society].”

“The prime minister is really critical – his leadership will be very important to a successful outcome,” he added.

Chile, which holds the current presidency of the UN climate process, also offered its support. Carolina Schmidt, who presided over last December’s Madrid climate talks, said: “Since the announcement that the UK will take on the presidency of COP 26, we have met representatives of the UK government on many occasions – including since the COP 25 meeting in Madrid. We look forward to continuing our close collaboration with the incoming COP 26 presidency, as well as other key partners, throughout 2020. This is a crucial year of climate action for humanity as a whole. We have a great challenge ahead: the climate crisis is a reality that all countries must tackle together, and we will stand firmly with our international partners to do so.”

Richard Kinley, former deputy head of the UN’s climate secretariat, said there was still time for the UK to recover. “Ideally, you would have started earlier, but politicians in the UK were preoccupied [with Brexit],” he said. “It is late but it is not too late for things to begin, but a lot needs to be done fairly quickly to build momentum for these talks. You need to get mobilised.”

As well as the lack of a president, there is a widespread sense that the UK has got off to a slow start in the all-out diplomatic push that is needed to bring reluctant countries together. “The UK diplomatic machine really needs to be running at full speed now,” said de Boer. “They need to be going to other capitals, finding out the key sticking points, and what needs to happen to get a high level of ambition. That’s only going to happen if you understand what the red lines are for all parties.”

Some developing countries said they were awaiting more details from the UK, including the identity of the new president. “Without a doubt it would be good that sooner rather than later we will know who our primary interlocutor will be for COP 26,” said a representative of one key group of countries.

Saleemul Huq, director of the International Centre for Climate Change and Development, added: “Every day that the prime minister does not have a COP 26 president in place is valuable time being lost”