• Video report by ITV News Political Correspondent Romilly Weeks

Boris Johnson vowed to tackle climate change as he launched a crucial summit on the issue, just hours after a blistering attack on his record by the event's sacked president.

The Prime Minister refused to answer questions as he entered the Science Musuem in London about who will replace former clean growth minister Claire O'Neill, the president of the UN COP26 summit in Glasgow at the launch on Tuesday.

Ms O'Neill heavily criticsed Mr Johnson's approach as he prepared to outline new measures to tackle climate change, including a ban on sales of new petrol and diesel vehicles being brought forward to 2035.

In a letter to Mr Johnson, where Ms O'Neill reveals she was sacked by Mr Johnson's adviser Dominic Cummings on Friday, she wrote: "You promised to ‘lead from the front’ and asked me what was needed: ‘Money, people, just tell us!’ Sadly these promises are not close to being met."

She added: "This isn’t a pretty place to be and we owe the world a lot better."

Claire O'Neill says she was fired by the PM's adviser, Dominic Cummings. Credit: PA

Ms O'Neill also claimed the Prime Minister had not convened the Cabinet subcommittee on climate change which he had promised to chair.

She added the Government was "miles off track" in setting a positive agenda for the summit in November, and that promises of action "are not close to being met".

Hours after the letter was published in the Financial Times, Mr Johnson was joined by David Attenborough at the launch at the Science Museum in London.

Mr Johnson told the audience: "We must reverse the appalling loss of habitats and species, it’s only by repairing the damage to the natural world and restoring the balance between humanity and nature, that is now so grotesquely out of kilter, we can address the problem of climate change.”"

The UN climate talks in November are the most important since the Paris Agreement to curb global warming was secured in 2015.

Pressure is also on countries to set out long-term plans for cutting emissions, with the science now clear that the world must reduce greenhouse gases to zero in a matter of decades to avoid the worst impact of climate change.

In her letter, Ms O’Neill suggested Mr Johnson’s personal animosity towards Scotland’s First Minister Nicola Sturgeon is endangering the success of the summit and claimed the Prime Minister is considering relocating the event to an “English location” because of “ballooning costs”.

Boris Johnson (left) and David Attenborough (right) at the Science Museum in London. Credit: PA

Ms O’Neill is also reportedly consulting lawyers about what she claims were “false, distorted and defamatory” briefings about her record, saying Number 10 was “rumoured” to be behind the briefings.

She told the Financial Times she had been considered for a peerage by Downing Street to give her more authority in her UN summit role, but this had now been “firmly rescinded”.