A man, draped in a Union Jack flag, was cheered on as the flag went up in flames close to Downing Street.
The crowd also jeered at around 300 pro-EU demonstrators who were walking from Downing Street to the office of the European Commission in London.
Police were seen forming a line to keep the two groups apart.
The pro-Brexit supporters sung “shame on you, shame on you”, “losers, losers” and “bye, bye EU” to the tune of Auld Lang Syne.
Meanwhile, dozens of people gathered around the Sir Winston Churchill statue on Parliament Square with at least one person dressed up as the former Prime Minister.
A music system was also been set up inside the back of a lorry on Parliament Street, with people dancing in a closed-off section of the street to music by Sir Tom Jones and Queen.
As one man walked through the crowd with an EU flag draped over his shoulders, another man carrying the Union flag shouted at him: “Go away loser.”
A modified Victorian cart featuring a small church bell and drum was responsible for much of the noise in Parliament Square.
Called Little Ben, the cart belongs to David and Nancy Waller, who have travelled down from Shropshire to take part in the Brexit Celebration.
Mr Waller, 59, said the cart cost about £500 to restore and build, thanks to a “Brexiteer” blacksmith who donated his services for free.
He said the bell, which people have been ringing throughout the evening, was found in a salvage yard but was originally forged at the Whitechapel Bell Foundry in London.
Mr Waller said: “We have come here because we are great supporters of democracy. At one stage we thought it was all over, but it ain’t now.”