The protest at H+K was undertaken by XR Cymru. Extinction Rebellion cited the agency's work for fossil fuel companies ExxonMobil, Shell, Chevron and Saudi Aramco, and for managing comms for Egypt’s presidency of the COP27 UN climate conference.
In response to criticism of its work with energy clients, H+K said: "Hill+Knowlton believes in the imperative to transition to a net zero future and is committed to playing a positive role in that process.
"While we respect differing opinions on this topic, we believe that constructive engagement with all those who are central to the transition, including energy companies, is essential for a transformation of this scale.
"As a company, we will not undertake any work that is designed to mislead people, or that downplays the importance of climate change, and we seek to represent the actions of our clients fairly and accurately at all times."
Other firms targeted included BP, BAE Systems, investment bank JP Morgan, law firm Eversheds Sutherland, petrochemical company Ineos, oilfields services provider Schlumberger, and insurance group Arch Insurance, with similar action taken.
The office of the Department for Business, Energy and Industrial Strategy on Victoria Street was also targeted over plans to issue new licences for the exploration and extraction of oil and gas in the North Sea.
Protestors also took action at the International Maritime Organisation, the Institute of Economic Affairs, and the Ontario Teacher’s Pension Plan. The latter is accused of funding investment in infrastructure projects including the expansion of Bristol Airport, which it owns.
Another campaign group, Christian Climate Action, took action outside Church House in Westminster to highlight what it said was the Church of England’s "failing strategy to stay invested in fossil fuels and influence the industry as shareholders".
The protests involved XR and other environment campaign groups including Plastics Rebellion, HS2 Rebellion, Ocean Rebellion, Money Rebellion, and Sky Rebellion.
Extinction Rebellion spokesperson Sarah Hart said: “While the rest of us worry about the cost of turning the heating on, our government is prioritising the profits of the very companies that are jeopardising our climate and environment. But everyday people are way ahead of politicians.
“Behind incomprehensible government decisions to double down on fossil fuel development, sign off new oil exploration licences and allow the big energy companies to rake in record profits, lies a network of companies and organisations that are profiting from this destructive path.”
The protests follow the conclusion of COP27 yesterday, which ended with almost 200 countries agreeing to a deal to launch a fund to support nations worst hit by climate change. There was criticism, however, of the lack of action to cut emissions.
This article was updated on Tuesday morning with a comment from Hill+Knowlton.