Environmental activists blocked the entrance to the headquarters of the company which owns the easyJet brand today, in a protest about the effects of short-haul flights on the climate.
A 12-strong group from the Plane Stupid campaign occupied the roof and six blocked the front entrance of easyGroup's offices in Camden, north London, police said.
The protesters also hung a banner from the roof which read: "End short-haul flights".
A Metropolitan police spokesman said: "We were called at about 7.30am after reports of protesters on the roof of the Rotunda. Around 12 males had also hung a banner from the roof. A group of around six people were also trying to stop staff entering the building."
The protest was part of Plane Stupid's national day of action against short-haul flights, which comes on the same day as the UN climate talks in Nairobi.
Andy Nash, a campaigner with the direct action group, said: "As warnings mount about the irreversible effects of climate change, it is totally out of order for Easyjet to be offering artificially cheap flights to destinations easily reachable by the train alternative, which is over 10 times less polluting."
The protest ended at around 10.40am, according to John Stewart, who is from the pressure group and took part in the demonstration.
He said: "We feel as though we have made our point, and made the point not just to easyJet, but to Tony Blair. Tony Blair talks the talk about taking action on climate change, while building more runways and allowing more planes at airports.
"Immediate action should be taken to deal with short-haul flights by increasing the tax charged on tickets for short-haul flights.
A spokesman for easyGroup said that around 20 staff had been delayed for about an hour and a half by the protest.
James Rothnie, director of corporate affairs for the group, said: "It has not really caused disruption to business. The airline easyJet functions out of Luton. We are the main shareholder in easyJet, but the management of easyJet is not based here."
EasyJet was founded by Stelios Haji-Ioannou in 1995.
The campaigners claimed they had also targeted around 25 travel agents across the UK last night, chaining their front doors and leaving signs on the windows which said: "Closed for a total rethink. See www.planestupid.com."
However, a spokesman for the Association of British Travel Agents, which represents around 6,000 travel agent branches, said today that none of its members had reported any damage.
At the weekend, more than 20,000 people rallied in London calling for action on climate change ahead of today's UN conference in Nairobi.
Today also sees the start of the World Travel Market (WTM), a major industry conference in London, which is holding its first World Responsible Tourism Day of Action this Wednesday. The initiative, backed by the UN's World Tourism Organisation, seeks to raise awareness of sustainable tourism issues and advise members of the travel industry on best practice.
Fiona Jeffery, WTM managing director, said: "It means the international travel industry can show en masse that it is actively making a difference in protecting environments, respecting local cultures, supporting local communities, conserving natural resources and minimising pollution."
