Cop26 will be the “world’s moment of truth”, Boris Johnson said as he urged leaders to use the Glasgow summit to bring about an end to climate change.

With the United Nations summit due to get under way on Sunday, the Prime Minister pressed fellow world leaders to seize the moment and deliver on the target of preventing global temperatures from rising by more than 1.5C degrees above pre-industrial levels.

Downing Street said Cop26 will be one of the biggest events the UK has ever hosted, with 25,000 delegates expected from 196 countries and the European Union.

Ministers, climate negotiators, civil society and business leaders are set to take part in talks and debates over the course of the two-week conference.

Mr Johnson, who is due to fly from the G20 in Rome to Glasgow on Sunday evening, said: “Cop26 will be the world’s moment of truth.

“The question everyone is asking is whether we seize this moment or let it slip away.

“I hope world leaders will hear them and come to Glasgow ready to answer them with decisive action.

“Together, we can mark the beginning of the end of climate change – and end the uncertainty once and for all.”

The Conservative Party leader has not struck an optimistic tone in the lead-up to the conference, repeating in interviews while in the Italian capital that he still rated the chances of success in Scotland as no more than six out of 10.

Prime Minister Boris Johnson has continued to suggest there is a six out of 10 chance of success at Cop26
Prime Minister Boris Johnson has continued to suggest there is only a six out of 10 chance of success at Cop26 (Jeff J Mitchell/PA)

His Labour rival accused the Prime Minister of “lowering expectations” in the run-up to the crucial negotiations with such comments, potentially putting Cop’s environmental targets at “risk”.

Sir Keir Starmer told the Sunday Telegraph: “The Prime Minister is turning into a commentator rather than a leader in relation to Cop26, lowering expectations by a commentary instead of (showing) leadership on the global stage.”

The Cop26 summit is aiming to urge countries to advance their net-zero commitments to the middle of the century and reduce emissions rapidly over the next decade through commitments on phasing out coal, switching to electric cars and planting trees.

Developed nations are also being urged to stump up the finance – 100 billion US dollars (£73 billion) per annum – needed by poorer nations to deal with climate change.

Number 10 said there is also a need to finalise the Paris Agreement at the event.

Cop26 president Alok Sharma told ITV News he would “like to see every country show more ambition”.

He added: “We’re at Halloween and what I would say to every country is that this is an opportunity to leave the ghouls, the ghosts in the past and look to the future.

“This is our opportunity at Cop26 to build on the commitments that we made, to get more commitments, but then also to demonstrate action because we are running out of time.

“This is the decisive decade, and countries and particularly world leaders have to act.”

The summit timetable will see the Prime Minister host an opening ceremony attended by dignitaries including the Prince of Wales, before giving a speech on Monday.

Charles and Sir David Attenborough, the Cop26 People’s Advocate, will be among those to also address world leaders as British environmental advocates.

The Duke and Duchess of Cambridge and Sir David Attenborough are all due to attend the Cop26 summit
The Duke and Duchess of Cambridge and Sir David Attenborough are all due to attend the Cop26 summit (Alberto Pezzali/PA)

The theme of the opening ceremony, due to take place at midday, is “Earth to Cop”, which Downing Street said would deliver a message from the people for leaders to heed warnings and advance progress to tackle climate change.

On Monday evening, the Prime Minister will host a reception to welcome world leaders to Glasgow, alongside the Duke and Duchess of Cambridge and the Duke and Duchess of Cornwall.

The Queen will address the delegates in a pre-recorded video after she was told by doctors to avoid the summit and rest following a hospital visit last week.

At the reception, guests will be offered refreshments of traditional Scottish canapes, Ridgeview vintage English sparkling wine and Cop26 blended whisky supplied by the Scotch Whisky Association.

Guests will enjoy music from a string quartet and brass quintet from the Royal Scottish National Orchestra.