Chuka Umunna is leading the march of the popular vote campaign through central London this afternoon, while the massive protest calls for a second Brexit referendum.
Hundreds of thousands of people are expected to fill the streets of the capital in what is considered the "biggest, noisiest and most important" demonstration of its kind.
However, Sky News anchor Gamal Fahnbulleh accused Chuka Umunna of "using the vote to nullify Brexit" when a fight between the pair erupted in a live interview today.
Mr. Umunna praised the "thousands of young people who lead the march," as he launched into the claim that a second vote was "undemocratic."
Mr. Umunna told Sky News: "Think about the argument that some people make, about" frustrating the will of the people ".
"How can it be undemocratic to have a vote from people who determine what we do in a Brexit agreement that looks very different from what people expected?"
"This has been a complete disaster, we are going to pay a divorce bill of 59 billion pounds with nothing in return and no guarantee of a future training relationship."
Sky News host Fahnbulleh challenged the Labor MP: "So, are you still asking for a democratic vote until you get the result you want?
"We already had a vote in 2016 and the prime minister has made it quite clear that we are not going to get another result."
"What is the point in this march?"
Umunna accused the television presenter of using an argument to "never have another general election" and added that "democracy is dynamic, changes with the times".
But Fahnbulleh replied: "It was the biggest democratic process that took place, but now he's saying, let's go back and make another decision about the vote he already had."
He added: "People will say, what you want is to prevent Brexit from happening.
"We have heard him say it over and over again and he is using the motives for another referendum to stop the Brexit process that received the approval of the British public."
Mr. Umunna admitted that the Brexiteers in 2016 "did not know why they voted".
He told Sky News: "I've always been clear that I want to stop Brexit, but I can not determine it."
The Prime Minister, Theresa May, has repeatedly ruled out a referendum of this type, the last of which will be held on Wednesday.
Richard Tice, founder of Leave Means Leave, called the demonstration this afternoon "a march of losers" and urged protesters to "accept that they lost."