Claire O’Neill, the former UK energy minister who was to lead the UN climate talks this year in Glasgow, has been removed from the post.

Her sacking comes as Boris Johnson prepares to launch the UK’s strategy for hosting November’s crunch climate talks, known as COP26.

O’Neill, under her Twitter handle of @COP26President, wrote on Friday evening: “Very sad that the role I was offered by Boris Johnson last year has now been rescinded as Whitehall ‘can’t cope’ with an indy COP unit. A shame we haven’t had one climate cabinet meeting since we formed. Wishing the COP team every blessing in the climate recovery emergency.”

The dramatic last-minute change of plan follows murmurings over the past month that O’Neill, known under her previous married name of Perry when she was a minister, lacked the gravitas for one of the most important jobs in international politics this year.

A source in the COP26 unit said: “Claire has seriously underperformed, including at Davos and on a recent ministerial visit to India. She had said ‘the Paris agreement is dead’ in key meetings to the surprise of everyone.

“She didn’t seem to get that this is a diplomatic job. The senior team of officials in the unit couldn’t work with her and her erratic behaviour and poor performance has spooked key stakeholders in the UK and internationally. She had to go. The PM now needs to show he is taking this seriously by appointing a heavy-hitting minister.”

Governments must come to COP26 prepared to scale up their commitments on cutting greenhouse gas emissions, or risk the failure of the 2015 Paris agreement on the climate.

Achieving the consensus needed among world governments will be a mammoth task – many countries, including the US, Brazil, Saudi Arabia and Russia, are now hostile to the Paris agreement, and others including China and India have been unwilling to make big new public commitments under the accord.

O’Neill’s previous experience peaked at junior minister, which was regarded by some diplomats as not enough to gain her the respect needed to get meetings with premiers and top officials around the world.

Observers of the UN talks interpreted her removal as a sign that Johnson was taking COP26 more seriously. He will make his first public intervention on the issue next Tuesday, when he will launch the UK’s COP26 strategy, at an event with Sir David Attenborough, the climate expert Lord Stern, the outgoing governor of the Bank of England, Mark Carney, the UN’s climate chief, Patricia Espinosa, and a host of dignitaries.

“A good COP president makes all the difference between success and failure,” said one former high-level diplomat and COP veteran. “They direct the negotiations, they play the key role in determining the outcome.”

Tom Burke, the co-founder of the environmental group E3G, said he thought that either William Hague or Michael Howard, both former Conservative party leaders, could be possible choices to replace O’Neill. “If this is a sign that the government really wants to signal its intent to make a success of COP26, it has to appoint some more senior people, and those two candidates come to mind,” he said.

Former foreign secretary William Hague is one of the names being touted to take on the role of COP26 chairman. Photograph: Andrew Parsons/ANDREW PARSONS

The Cabinet Office, which has been leading on the COP26 talks, declined to say whether a successor had been chosen. There have been rumours among climate activists that Zac Goldsmith could take on the role, and O’Neill’s tweet appeared to suggest that responsibility for COP26 could be taken away from the Cabinet Office.

The Cabinet Office put out a statement: “Claire Perry O’Neill will no longer be UK COP26 president. The prime minister is grateful to Claire for her work preparing for what will be a very successful and ambitious climate change summit in Glasgow in November. Preparations will continue at pace for the summit, and a replacement will be confirmed shortly. Going forward, this will be a ministerial role.”

That could leave the way open for a House of Lords appointee.

Responsibility for the UK’s participation in the annual talks was previously held by the Department for Business, Energy and Industrial Strategy, after the closure of the Department of Energy and Climate Change.

Another COP expert said whoever took on the job must have the clear and public backing of the prime minister, and that Johnson must take a much stronger public role on the issue.

In her parliamentary career, O’Neill was best known for having to apologise when, unable to catch the Speaker’s eye, she wondered aloud in the House of Commons to whom she needed to “give a blowjob” in order to get her say.

She also issued a putdown to David Davis when he confused her with another female Tory minister, Caroline Nokes. Referring to Davis’s previous campaigning slogan, she is reported to have told him: “David, let me help you: Caroline is a C cup, I am a double D.”

Her exuberant manner also led to trouble. In November 2018, three unions wrote to BEIS, where she was a minister, to raise allegations of shouting and bullying civil servants.

O’Neill started out as a political radical. The environmentalist George Monbiot recalls her at Brasenose College, Oxford, where she studied geography, as “a leftwing firebrand who wanted to overthrow capitalism and nationalise the banks. She was impressive and persuasive, and had some influence on my thinking. You can imagine my disappointment when she took a City job and became a Tory.”

She entered parliament with the coalition government in 2010, her no-nonsense approach belying the patronising “Cameron cutie” label.

O’Neill announced her decision to resign as an MP last September, citing the pressures of the COP26 presidency, and she stood down in December’s election. That left her free to jet to foreign capitals, but outside cabinet discussions.

Johnson’s government is vulnerable to charges that ministers are not prepared to make the hard decisions required against vested interests in fossil fuels and finance. There was a major hiccup at the Africa summit last week when, as Johnson pledged not to invest in coal in Africa, the Guardian drew attention to the almost £2bn finance from the UK pouring into African oil and gas.