Anti-Brexit protesters have travelled from all over the country to London for the 'Put it to the People March' as the online petition urging the government to cancel Brexit passed four and a half million signatures.
Opponents of Britain's departure from the European Union began gathering in Hyde Park from 12pm before converging on Westminster and organisers claim a million people turned up to voice their concerns over the decision to leave the EU.
If true, today's demonstration would be the biggest since 2003 when an estimated one million people protested against the Iraq War in the streets of London.
Other speakers included former Conservative cabinet minister Justine Greening and ex-attorney general Dominic Grieve, former Tory turned independent MP Anna Soubry, Lib Dem deputy leader Jo Swinson, Green Party MP Caroline Lucas and SNP Westminster leader Ian Blackford.
Organisers claimed that one million protesters came to the protest, after previously saying they were confident that the size of the crowd would exceed a similar rally held in October, where 700,000 people turned up.
The Metropolitan Police refused to comment on the size of the march.
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People attended the march in London carrying signs we read 'we are European' and 'this doesn't seem very well thought through' while other carried a sign with the poo emoji
Thousands of people gathered in Hyde Park from 12pm before converging on Westminster to take part in the Put It To The People march
Independent Group MPs Chuka Umunna and Anna Soubry have a selfie taken with actress Tracey Ullman as they join anti-Brexit campaigners taking part in the People's Vote March
Organisers of the march claim a million people joined in on the 'People's Vote' demonstration through the streets of London
Prime Minister Theresa May was unsurprisingly the target of many of the protests, with some coming up with some creative ways to show their anger
The exact number of people at the march has yet to be determined but photos show large crowds and organisers are confident the final number will be more than 700,000
A demonstrator sits on one of the lions in Trafalgar Square during the march. The young man holds an 'I love Europe' sign
Addressing the crowd in Parliament Square, Labour's deputy leader Tom Watson said: 'We are one million strong.'
He said he was there on behalf of his 10-year-old daughter.
'She has told me to thank you for campaigning for her future,' he said.
Mr Watson said the Prime Minister's deal 'pleases no-one'.
'If you voted remain it's a rubbish deal, if you voted leave it's a lousy deal. There are no winners, only losers,' he said.
He added: 'Brexit is stuck in the parliamentary pipeworks and it's not going to find a way out.'
Addressing his comments to Theresa May, he said: 'I can only vote for a deal if you let the people vote on it too.
'Prime Minister, you've lost control of this process, you're plunging the country into chaos, let the people take control.'
Trains, coaches and buses were chartered to bring as many people as possible, from all around the country to today's anti-Brexit march in London
A demonstrator paste an anti-Brexit sticker by the entrance of the UK government's Cabinet Office during today's protest
Anti-Brexit placards are placed outside the entrance to the Cabinet Office on Whitehall during march. The march was organised to go from Park Lane to Parliament Square
EU supporters, calling on the government to give Britons a vote on the final Brexit deal or reverse Brexit entirely, descend on the capital to protest
An anti-Brexit protester carries his child on his back during today's protest, while she holds up a sign saying 'May I have my future back please'
One protester holds a placard which says 'IKEA has better cabinets' and another reads 'too young to vote... not too young to remember'
'Brexit is a complete and utter mess,' Khan said on the eve of the event.
'I'll be marching on Saturday with people from every part of our country - from every walk of life - to demand that the British people get the final say.'
Labour's Jess Phillips also attended the march with her son.
Following the event, the Birmingham Yardley MP tweeted: 'I was worried about taking my kid to #PutItToThePeople I have to consider his safety and our security but there was not even the tiniest sign of trouble.
'The nicest march I ever attended.'
Earlier, former Ukip leader Nigel Farage joined the counter March to Leave in Linby, Nottinghamshire, telling around 200 Brexit supporters that Theresa May had reduced the nation 'to a state of humiliation'.
The 'People's vote' protest - expected to be one of the largest in the capital in decades - was hosted by the People's Vote pressure group.
Organisers arranged hundreds of coaches and even chartered a train to bring protesters from all corners of the country to the capital.
Among those in attendance was Stephen Goodall, a 96-year-old World War II veteran, who travelled 200 miles by train from southwest England alongside four generations of his family including his great-granddaughter.
Organisers have arranged hundreds of coaches and even chartered a train to bring protesters from all corners of the country to the capital
This seven-year-old boy joined in with today's protests and was one of many young people to take part and march towards Parliament
A placard has an image of Jacob Rees Mogg, Nigel Farage and Boris Johnson made up as clowns on it and has surrounded them with EU flags
Aerial shots of the protests show the thousands marching through central London to demonstrate against Britain's decision to leave the EU
There was a huge turnout at the march and campaigners arrived in the capital from across the country, with one taking on a 715-mile journey on ferries, trains and buses from Orkney in Scotland
An unnamed protester was pictured wearing a European Union flag on her top and waving a flag during the march
The protest officially started at Park Lane but people from several locations all over London joined up with the main march as it descended on Parliament
A general view of Anti-Brexit campaigners as they take part in the People's Vote March in London and wave pro-EU banners
Three protesters on the march wear blue and yellow-coloured clothing to show their support for the European Union in the face of Brexit
There were a sea of flags and banners at today's march, with organisers claiming a million people turned out - though police have yet to confirm
Two men draped in EU flags look at a mass of placards outside the Cabinet Office in Whitehall during the march through the capital
'I am an old man and the outcome won't affect me - but it will affect my family and many people that I know for years to come,' he said in a statement released by organisers.
The marchers also included 63-year-old Edmund Sides, who spent the last three weeks walking from Wales to London in order to take part.
Mr Sides, a geologist, said he wanted to be able to speak to people along the way, encouraging families that have been split between Leave and Remain to mend fences and talk.
'The whole country isn't doing enough of that,' he said.
Mr Sides is worried about the vicious tone that arguments have started to take and worries about national cohesion. Walking gave him a chance to talk to people along the way, and see what others were thinking.
'People fear the atmosphere is very dangerous in this country,' he said.
Campaigners arrived in the capital from across the country, with one taking on a 715-mile journey on ferries, trains and buses from Orkney in Scotland.
Student Sorcha Kirker, 27, was joined by about 30 other students from the University of the Highlands and Islands.
Young members of the Conservative party also turned out to protest against Brexit, joining in with socialists and others to protest against Brexit
The 'People's vote' protest - set to be one of the largest in the capital in decades - is hosted by the People's Vote pressure group
People hold up placards and European flags as they attend a march and rally organised by the pro-European People's Vote campaign for a second referendum
Saturday's protest follows a similar demonstration in October that drew an estimated half a million people, as an online petition urging the government to cancel Brexit passes four million
The protest comes after EU leaders this week granted a delay to Brexit, prompting Theresa May to make another attempt to get her Brexit deal through
This dachshund, or sausage dog, wears a banner on its coat with the words 'Brexit is the wurst' as it joins in on the protest in London today
The protest comes after EU leaders this week granted a delay to Brexit, prompting Prime Minister Theresa May to make a renewed bid to win MPs' backing for her divorce deal.
However, she faces daunting odds with lawmakers deadlocked for months over how to implement the 2016 referendum vote to leave, reflecting bitter divisions nationwide.
If she succeeds, Britain - which was staring at a cliff-edge deadline of March 29 for leaving the EU - will depart on May 22 under the terms of the withdrawal agreement the prime minister struck with Brussels last year.
But if lawmakers defeat the accord again, as expected, London must outline a new plan or face a no-deal Brexit as early as April 12 - unless it decides to request another extension and hold European Parliament elections in May.
Protesters on the Put It To The People March, demanding the public is given a final say on Brexit as they make their way through Piccadilly
Young girls join the protest against Brexit in London today, holding signs in favour of the EU and lending their voices to calls for another referendum
An anti-Brexit and pro-socialist banner is unfurled and hung from Westminster Bridge before today's march in London started
People young and old turned out for the anti-Brexit march and rally, including actor Eddie Marsan and his family who are all wearing T-shirts supporting the EU
Chuka Umunna and Anna Soubry took centre stage during the protest, wearing shirts expressing their support for the march as they were surrounded by anti-Brexit campaigners
A demonstrator leads a dog wearing a suit in the EU colors during the Peoples Vote and anti-Brexit march that started at noon today
A man wrapped in an EU flag watches on as the thousands of people in the crowd make their way through London during the march
This woman was one of many holding up banners and signs calling for Article 50 to be revoked and Brexit to be cancelled
Organisers of the march claim a million took to the streets of central London six days before the UK is due to leave the EU
This teenager was one of many young people to take part in today's march and defend another referendum from the government
Any further delay would likely prompt further calls for another referendum as the only way out of the impasse.
The prime minister has repeatedly ruled out holding another poll on the issue, claiming it would be divisive and renege on promises to honour the 2016 referendum result.
Meanwhile the main opposition Labour Party appears divided on the issue.
At its 2018 conference, it backed holding another poll as a last resort, while advocating staying in a customs union with the EU together with close alignment with its single market.
Anna Soubry MP taking part in today's march and being enthusiastically greeted by a fellow protester, who is wearing a 'Stop Brexit' hoodie
Protesters brought homemade banners and placards to the march with one saying 'pull out doesn't work' referring to the country's decision to leave the EU
Anti-Brexit marchers said the decision will affect future generations while others brought placards saying 'Cats against Brexit'
This protester is calling for the nation to be 'given a final say'. Using the famous catchphrase of the famous Star Trek character Spock, he believes that Britain should 'remain and prosper'
As well as campaigning against Brexit, this protester took the time out to express his dissatisfaction with the leaders of both of the UK's main parties
Thousands of people pictured taking part in the march while waving pro-EU slogans, EU flags and anti-Brexit placards
One protester waved a placard bearing Edvard Munch's iconic painting of The Scream with the word Brexit! emblazoned above it while another had a picture of Brexiteer Jacob Rees-Mogg saying 'Mogg off'
A girl with a placard 'We Shall NOT be MOGGed!' attends the 'Put it to the People' march in London, in criticism of Tory MP Jacob Rees-Mogg
One protester referred to Theresa May's slogan in the run-up to the 2017 election referring to her 'strong and stable' government
Dogs seemed to be present at the march in abundance, with this one also wearing a sign that is critical of Brexit
A woman with yet another dog and banner which reads 'No Hard Borders! They're not nice' attends the 'Put it to the People' march in Trafalgar Square
But some MPs are fierce advocates of putting it back to the people, while others representing Leave-supporting areas in central and northern England, are bitterly opposed.
In a sign of the splits, at least half a dozen Labour shadow ministers were expected to join deputy leader Tom Watson at Saturday's march, while the party itself asked activists instead to help campaign for local elections due on May 2.
Watson said he had now decided to campaign for a referendum 'reluctantly' and would back May's deal if it was also put to the people.
'It can only begin to bring the country back together again if we all have a final say - and then live with the result,' he said.
'I trust the people I represent. And only they can sort this mess out.'