A Green Party council leader has apologised "unreservedly" after he flew to the COP26 climate summit in Glasgow.
Phélim Mac Cafferty said the decision was a "major failure" of his judgement which "goes against" his political group’s "pledges and principles".
Some have called for the Brighton and Hove City Council leader to resign following the revelation.
Phélim Mac Cafferty took a plane from London to Glasgow because of concerns about the "unreliability of the rail network".
He says he will "offset the carbon cost" of the journey and returned by train.
Phélim Mac Cafferty's full statement: "On 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.
"I reluctantly took this very difficult decision because I was concerned about the unreliability of the rail network following the well-publicised difficulties experienced by many people wanting to travel by train to Glasgow the week before, when trains were cancelled.
"I was concerned that this would happen again and I felt it was important not to miss the opportunity to attend the important presentation on behalf of the city, lobby world leaders and share with others the innovative work taking place in Brighton & Hove.
"I paid for my own transport and all associated costs. I am not getting paid for any of the speeches I am making or meetings I am attending and I am otherwise working from Glasgow.
"Transport contributes a large portion of carbon emissions, all significant journeys we make have an effect on our climate. I will be offsetting the carbon cost of my journey.
"I will be taking my return journey on train.
"Again, I apologise unreservedly."