Boris Johnson will make a day trip to the Cop26 climate summit in Glasgow on Wednesday to urge climate negotiators to “pull out all the stops” – travelling by train, after he was criticised for flying back by private jet last week.

The prime minister attended the opening days of the summit with scores of other world leaders before returning to Westminster and leaving the Cop president, Alok Sharma, to oversee the complex negotiations. He will attend on Wednesday but is not set to be in Glasgow at the end of the summit this weekend, as some had expected.

“I’ll be meeting with ministers and negotiators to hear about where progress has been made and where the gaps must be bridged,” the prime minister said in remarks released before his visit.

“This is bigger than any one country and it is time for nations to put aside differences and come together for our planet and our people. We need to pull out all the stops if we’re going to keep 1.5C within our grasp.”

Some progress was made last week on specific issues such as deforestation and the phasing out of coal. But in the broader negotiations, there are concerns about both the scale of the emissions pledges made, and when they should be updated, with some countries keen to see an annual process.

A report published by the respected Climate Action Tracker (CAT) coalition on Tuesday suggested the 2030 goals set by countries at the summit could put the world on course for a catastrophic 2.4C of heating by the end of this century.

In a press conference at Cop last week, the prime minister described himself as “cautiously optimistic” about the outcome of the summit but called on countries to be more ambitious.

There had been some suggestions Johnson would attend the final stages of the negotiations. These are due to end on Friday but previous Cop gatherings have often stretched well into the weekend, and Johnson is due to mark Remembrance Sunday in London.

Downing Street has therefore decided the prime minister will attend on Wednesday only.

The Liberal Democrat leader, Ed Davey, said Beijing, not Glasgow, should be the target of Johnson’s last-minute bid to energise the talks.

“The UK must unite the west to get China into a better place,” said Davey, a former energy secretary. “If Glasgow’s Cop fails, we will be letting down future generations and the sense of anger and frustration in our country will be palpable. Failure is not an option.”

The prime minister is travelling by train after being criticised for flying back to London last Tuesday and attending a dinner with the former Telegraph editor Charles Moore, a climate sceptic.

While delegates in Glasgow have continued discussing the planet’s future, Johnson has been embroiled in a sleaze scandal after whipping his MPs to support a bid to protect veteran Tory MP Owen Paterson from being punished for paid lobbying. Paterson has since resigned.

The House of Commons is on a short recess from Wednesday until next Monday, so Johnson will not miss a session of prime minister’s questions.