Phelim Mac Cafferty jumped on a flight to Glasgow last Friday night ahead of an appearance at the summit on Saturday. He lectured on the need to cut carbon emissions and attended a protest march led by Greta Thunberg.
His 460-mile journey came on the same day he lambasted the Prime Minister and other world leaders for failing to stop “climate chaos”.
He also bragged about how under his leadership, Brighton and Hove council were “leading the way” and setting an example on how to deal with climate change.
“With all eyes on the world’s climate conference happening in Glasgow, there is hope – but also concern – that world leaders will fail to take the bold action needed to truly avert the climate crisis,” he wrote for the local paper, The Argus, last Friday.
“We need world leaders to act and to unlock the resources our communities need to prevent the worst of climate chaos.
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“Despite a lack of action from national government, councils like ours are leading the way – including in areas that have been shamefully left out of the bigger climate conversation.”
Mr Mac Cafferty co-chairs Brighton and Hove City Council’s carbon-neutral working group.
He has now apologised for breaking the rules, describing it as a “major failure of judgement”.
The council leader told The Argus: “In the Friday evening just gone, I took a flight from London to Glasgow to attend COP26 where I had been invited to represent the city at a presentation of the Glasgow Declaration on Saturday morning.
“This decision to fly was a major failure of my judgement which goes against my political group’s pledges and principles and I unreservedly apologise.”
He claimed he made the decision due to fears over the reliability of the train network.
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“I will be taking my return journey on train.
“Again, I apologise unreservedly.”
Mr Mac Cafferty had criticised the Government for cutting the cost of domestic flights in the Budget.
Last month Chancellor Rishi Sunak announced he was lowering domestic air duty while increasing tax on “ultra long haul” flights.
The Green council leader said at the time that the plans “simply don’t make sense as world leaders meet in Glasgow” to discuss climate change.
COP26 is in its second and final week of meeting, as world leaders look to thrash out a deal to keep hopes alive of limiting temperature increases to 1.5C by 2050.
The latest national plans by countries for action on cutting emissions this decade still overall leave the world far off track to meet the internationally agreed goal.
Scientists say greenhouse gas emissions must be halved by 2030 in order to on track to meet the 1.5C limit.