Environmental campaigners have reacted with fury, saying many of the journeys could have been undertaken on regular passenger aircraft, or even by train in some cases.

Mr Johnson flew to Glasgow on a private jet from the G20 summit of world leaders in Rome, where he had lobbied fellow leaders on global warming ahead of Cop26. He will use the same mode of transport to return to London later this week after delivering his speech on Monday.

The Prime Minister’s spokesman said: “Obviously the fuel we use for this flight is sustainable and emissions are offset as well. It’s important that the Prime Minister is able to move around the country and obviously we have faced significant time constraints.”

Private jets ‘by far the most polluting’

Matt Finch, of the Transport and Environment campaign group, pointed out that only 35 per cent of the fuel used by the Prime Minister’s aircraft was “sustainable”, with the rest being traditional hydrocarbons.

Even “green” aviation fuel contributes to global warming through other pollutants including water vapour, which forms heat-trapping clouds.

He said: “Private jets are by far the most polluting form of transport. Using them to get to and from a climate conference sends out completely the wrong message, and questions need to be asked of the politicians that use them.”