An Extinction Rebellion climate protest at the Cenotaph on Remembrance Day was “profoundly disrespectful”, the Prime Minister’s spokesman said.

Boris Johnson’s spokesman joined a chorus of disapproval over the actions of climate protesters who unveiled a banner reading “Honour Their Sacrifice, Climate Change Means War” at the memorial on Whitehall, in central London on Wednesday morning.

After the banner was displayed, British Army veteran and Extinction Rebellion member Donald Bell observed a two-minute silence before hanging a wreath of poppies bearing the message “act now”.

But the timing of the stunt has drawn criticism, and the spokesman for the Prime Minister said: “The Cenotaph is a memorial to those who fought and died to preserve all our freedoms.

“On today, of all days, when we join together to pay tribute to our war dead, this action was profoundly disrespectful.”

Asked whether officers should have prevented the stunt, the spokesman said: “These are operational matters for the police.”

Sir Keir Starmer also criticised the campaigners for acting “in bad taste”.

A spokesman for the Labour leader said: “No one can doubt how serious the climate emergency is, but the protests at the Cenotaph are wrong.

“They are in bad taste. We do not support them.”

The Royal British Legion (RBL) also hit out at the group’s stunt, saying the day was not a time for political protest.

An RBL spokesman said: “War memorials and graves honour the memory of every member of the Armed Forces who has made the ultimate sacrifice and deserve to be treated with the utmost respect.

“The Armed Forces community, past and present, have made sacrifices in defence of the freedoms we have today, including the freedom of speech.

“While we respect the right of others to express their opinions within the law, we believe the Poppy Appeal is a time for remembrance, and not for political protest.”

Veterans minister Johnny Mercer tweeted: “Climate change matters, but the Cenotaph on Armistice day should be about one thing only – showing our respect for the sacrifice of the fallen who died to protect our freedoms today.”

Protester Mr Bell, 64, who completed four tours in Northern Ireland during the Troubles, said his actions were in response to the Government’s “‘Dad’s Army'” approach to protecting the country from climate change.

He said: “Unchecked climate change means a return to a world at war.

“I took action today knowing that I would be criticised.

“I knew that I would be accused of being disrespectful and hated by many for speaking out in this way. Remembrance Day is never an easy time for veterans and this was not an easy decision for me to make.

“This Government’s own climate advisers, the Committee on Climate Change, said last year that they have a ‘Dad’s Army’ approach to protecting British people from the impacts of climate change.

“Their report in June this year showed that the Government has failed to meet all but two of the 31 milestones it set itself for reducing emissions.

“This Government is criminally negligent and young people today will pay the price for their failure.”

Metropolitan Police officers moved in to remove the Extinction Rebellion wreath after it was placed on the monument.

Force boss Commissioner Dame Cressida Dick said she is reviewing how the officers dealt with the protest.

She told the London Assembly Police and Crime Committee: “Activity this morning was clearly very offensive to many people. The actual wording on the banner is not of itself offensive, but to go to the Cenotaph for a protest of any sort would have been offensive for many people.

“I am reviewing what happened there. What I can tell you is whoever it was that left the banner was there I believe at 8am, it was removed as soon as the officers saw it at 8.20am.

“I of course like everybody regret the fact that people have seen it fit on today of all days to put an inappropriate banner around the Cenotaph.”

Officers are investigating any potential breaches of coronavirus lockdown rules.