Environmental protesters blocked the path of Boris Johnson’s car on Wednesday as he made his way to Buckingham Palace to officially become Britain’s new prime minister. The protesters said they were aiming to highlight the need to tackle the climate emergency.

The Greenpeace activists joined hands across the Mall as Johnson was making his way to meet the Queen. The protest, in which the activists had planned to hand a letter to Johnson that detailed how to end the climate crisis, was quickly broken up by police.

The former Green party leader Natalie Bennett said on Twitter that the event was “a reminder for Boris Johnson, in case the air-conditioning was making him forget”. She added that the climate emergency “should be at the top of his in-tray”.

The protest came just before the Queen asked Johnson to form a government, after Theresa May’s resignation as prime minister and his victory in the Conservative leadership contest on Tuesday.

On Wednesday evening, hundreds of people gathered in Russell Square in London to protest against Johnson’s ascension and the government.

The demo, dubbed “fck govt fck boris” after a lyric from Stormzy’s Vossi Bop and billed as a street festival, featured a bus with the words emblazoned on it as a nod to Johnson’s “£350m for the NHS” promise on the side of the Vote Leave campaign bus.

The Labour leftwing grassroots movement Momentum, the Women’s Strike Assembly and Guardian columnist Owen Jones were among the event’s organisers.

After a DJ set and performances from musicians, the demonstrators began marching through central London towards Trafalgar Square. Later, a group of protesters, more than 10,000 according to organisers’ estimates, marched south to the gates of Downing Street, many of them chanting: “Boris Johnson, fuck off back to Eton.”

Joey D'Urso (@josephmdurso) A very profane protest against Boris Johnson pic.twitter.com/LfqIajFUkZ

Downing Street was put into lockdown as the gates were blockaded by about 100 officers and a dozen riot vans, and no one was allowed in and out of that entrance. Meanwhile, the anti-Johnson campaigners set off purple and pink flares as they danced to booming music.

Just before 8pm, MP Grant Shapps turned up at the Downing Street gates, where he was promptly turned away by an armed officer on duty.

On the other side of the gates, and away from the demonstration, a string of tight-lipped Tory MPs made their way out of No 10 as further appointments were announced. They each walked straight from No 10 to a private exit which took them towards the Foreign Office buildings or a back exit.

Shapps eventually used a different route to No 10, where he learned that he had been made transport secretary.

The shadow chancellor, John McDonnell, earlier gave a speech in Russell Square in which he described Johnson as a “racist” and “a liar”. He also warned onlookers not to “fall for his buffoonery”.

Play Video 1:57 'Fck govt fck Boris' protest takes place on PM's first day in office – video

Lois Ward-Marvin, 23, a tattoo artist, was among the demonstrators. She said: “I don’t want Boris Johnson to be prime minister – the people that did vote for him were all white men. He’s racist, sexist, homophobic, and I don’t think he really wants to bring change for good.”

However, Ward-Marvin added that she did not know who in politics would be a better fit for the post. “I’m Jewish, so the antisemitism row has pushed me away from Labour,” she said.

Also in the crowd was lecturer Kevin Logan, 54. He said he was protesting against Johnson’s “incompetence”. He added: “He’s going to be awful and I’m really scared of what’s going to happen with Brexit with him in power.”

Facebook Twitter Pinterest Demonstrators gather outside Downing Street in London. Photograph: Hannah McKay/Reuters

Speaking close to Downing Street, Jay Crosbie said he was at the protest because he believed Johnson’s time in government would be “detrimental” to the country. “I’m here as a queer person – we know we’re the people he doesn’t care about,” he said.

Instead of a banner, Crosbie carried a rainbow fan with the words “bum boys” written between the folds as a nod to an infamous comment by Johnson.

Crosbie was not only worried that things such as the controversial Gender Recognition Act “won’t be on the table” under Johnson’s premiership, but also that he would not be able to resolve the current Brexit chaos. “The enormity of this just seems lost on Boris Johnson – it’s like a pantomime, like Punch and Judy,” he added.

Despite the anger at the new prime minister, the demonstration appeared overall to be peaceful and there were no arrests. A second protest is planned for 20 September.

Earlier in the day, campaigners from People’s Vote UK held banners outside Parliament Square and Buckingham Palace to urge the government to give the public a vote on the final Brexit deal.