Dozens of campaigners blocked the roads around Parliament Square to highlight concerns about the environment on Saturday.

About 50 activists from Extinction Rebellion, a direct action group that has been coordinating a campaign of civil disobedience which has brought areas of the capital to a standstill in recent weeks, risked arrest by standing defiantly in roads in front of queueing traffic.

An estimated 1,000 more demonstrators, many clad in black clothing, massed on the green in Parliament Square for what organisers labelled a “memorial service” to mourn the loss of life on the planet.

Many waved banners emblazoned with slogans including “System change, not climate change” and “Rebel for life” as they listened to speeches.

One older woman superglued her hands to a railing outside Buckingham Palace in protest. Scotland Yard confirmed that 14 protesters had been arrested for criminal damage during the day.

Campaigners said the protest, named “Rebellion Day 2”, aimed to highlight “the government’s failure to recognise and act on the ecological and climate emergency”. It follows similar events last weekend, when 82 people were arrested following staged sit-ins on five bridges crossing the Thames.

Facebook Twitter Pinterest Nicki Myers at the protest in Parliament Square on Saturday. Photograph: Simon Murphy

Among the campaigners blocking four roads entering Parliament Square on Saturday was Nicki Myers, 45, from Cambridge. Myers, who uses a wheelchair and suffers from the lung condition pulmonary fibrosis and Ehlers-Danlos syndrome, said she was prepared to be arrested in the attempt to raise awareness about the environment.

Sitting in front of traffic and clutching a banner with the slogan “Rebel for life cos we can’t breathe”, she said: “I’m mostly here for my granddaughter, Isabel. I’m terrified about of the prospect of society breakdown in her lifetime. I want the government to tell the truth and do something.”

She said she was ready to be arrested to bring about a change in policy “if that’s what it takes”, adding: “I’ve never done anything like this before. It’s quite scary.”

Lying down in the road nearby with his head resting on a backpack, 82-year-old protester Phil Kingston said he too was prepared to be arrested in the name of raising awareness for the environment. The pensioner, a retired university lecturer, said he had been arrested three times during Extinction Rebellion demonstrations in the past fortnight.

“I have four grandchildren and nothing is more important to me than their security,” he said. “And that security is being eroded all the time by an economy that is pumping fossil fuels in the air when already we are heading for disaster. I’m not accepting it. I don’t mind going to prison.”

Play Video 13:39 'We can't get arrested quick enough': life inside Extinction Rebellion - video

A young woman called Zappi, who did not wish to give her second name, also said she was willing to be arrested despite acknowledging the potential for it to harm her future prospects. The student, holding one end of a large sign reading, “Tell the truth”, said: “I feel like getting arrested is very small compared to the fact that potentially we could destroy our planet.”

Helen, 43, travelled from Ipswich with her four-year-old daughter, Lucy, to join the demonstration for the day. Sitting on a blanket in Parliament Square, the court transcriber said: “The truth is that the world is collapsing environmentally. The state of the world has become serious. The government seem almost insane in the way they are completely ignoring it. I’d like to see them treating it like it’s an emergency.”

A second world war memorial in Whitehall, honouring the work of women during the conflict, was graffitied during the protest. Other campaigners later rubbed off the spray-painted message, which read “MOTHER”. Scotland Yard confirmed that a suspect had been arrested on suspicion of criminal damage in relation to the graffiti.

Facebook Twitter Pinterest Police and protesters remove graffiti from the memorial to the women of the second world war in Whitehall. Photograph: Simon Murphy

The 6.7-metre (22ft) bronze sculpture, which cost £1.3m, was unveiled by the Queen in 2005 to pay tribute to the millions of women who contributed to the war effort.

After spotting the graffitied war memorial, campaigner Catherine Jones rushed to a local shop to buy nail polish remover and cotton pads to clean it off. The hospital worker, who helps run arts activities for patients, told the Guardian she did not want the graffiti to detract from the message of the day.

Jones, who brought her one-year-old daughter, Louise, to the demonstration, added that she did not agree with the graffiti. “I just don’t like it. It’s not helpful,” she said. “I think the day should be remembered by the performing element of it, which I thought was phenomenal. The message is strong. Yes, we are going to disrupt the traffic and yes, we are meant to get people a little bit annoyed at it.”

Activists were also spotted daubing graffiti on the road outside Downing Street.

During the protest, campaigners carried a mock coffin in a funeral-style procession and took part in a mass sit-down protest for around 10 minutes outside the gates of Downing Street, chanting: “Climate justice, when do we want it? Now.” Several protesters also lay down in front of the gates.