The big-spending chancellor, in whose largesse many observers detected the hand of his boss, Boris Johnson, cut air passenger duty for domestic flights and offset that by hiking charges on long-haul international trips.
He was swiftly accused of undermining Britain's climate credentials ahead of Cop26, with Friends of the Earth branding his decision "retrograde".
On Sunday the head of the government's advisory climate change committee, Lord Deben, claimed the tax was calculated to cast the UK's decision to leave the European Union in a positive light.
He told Sky's Trevor Phillips on Sunday: “I'm afraid the government is hung up in trying to prove that leaving the European Union was a good idea.
“And that's quite difficult. So one of the things it can do is to reduce the taxes internally and not across the whole of Europe. So, he decided to do that.
“Actually, it doesn't make any difference. As a matter of technicality, because the way that internal flights are accounted for under climate change will mean that they'll just have to pay more in carbon.”
The Conservative peer added: “So, it's not carbon tax. So, actually, it's not going to make all that difference. But it was perhaps not the right thing to do. I think it's less important than remembering that they have increased the cost of long-haul flights.
“And remembering also that the biggest mistake that was made was to cut our overseas aid to 0.5 from 0.7, which doesn't give people confidence that we are going to help people in the way we've promised to do. That, for me, was a really deeply immoral and unacceptable act.”
Lord Deben was speaking on the opening day of Cop26, the UN climate summit being hosted in Glasgow. Earlier on Sunday he had described the two-week convention as “the one chance we have to save the world”.
Additional reporting by PA Media
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