Thousands of demonstrators have gathered in London to protest Britain's departure from the European Union as Europe's Treaty of Rome statute celebrates its 60th anniversary.

Protesters will march to Parliament days after a terrorist attack in the same spot claimed the lives of four people and Khalid Massod the London attacker, sparking security concerns and debates as to whether the march should proceed.

However, with a heavily armed police presence on site, organisers decided to go ahead with the aim of sending Prime Minister Theresa May a strong message as she gets set to trigger Article 50 this Wednesday (29 March).

"Fundamentally, we never wanted Brexit and this march is about making our voices heard," a spokesman for the Unite for Europe march said in a statement.

"The voices of those who believe it's not okay to ignore us, it's not okay to incite hate and divide communities and it is not okay to fail to protect EU nationals who work and pay taxes in the UK.

"The voices of those who believe it's not okay for a handful of people to decide the future of many behind closed doors, it is not okay to lie and put futures at risk for political gain and it's not okay for the old to decide the future of the young.

"If Article 50 is triggered we'll do everything we can to stop the damage this government is causing."

Dr Mark Unitt, a 62-year-old retired IT consultant from Cardiff, is among those attending the protest.

He told IBTimes UK: "Almost half the population voted to remain and we're not represented – that's why I'm here today.

"Those of us who voted Remain haven't changed our mind, but a lot of people who voted Leave have."

Politicians including Liberal Democrat leader Tim Farron, Nick Clegg and Alastair Campbell are all due to address crowds and argue why the views of the 48% who voted to remain must not be ignored.

Addressing the audience, Farron said: "We are not giving up this week of all weeks. We here are as testament that we refuse to despair. Britain can be better."

Prior to the protest beginning, a moment of silence was held in memory of those who lives' were lost on Wednesday (22 March) and dozens of people laid floral tributes next to Parliament.

tributes Westminster
Floral tributes laid next to Parliament in memory of the four people killed in Wednesday's terror attack. Reuters
Armed police officers stand at the Carriage Gates entrance to the Houses of Parliament, following the attack in Westminster earlier in the week. Reuters