Palace of Westminster, the London Eye and other key landmarks were lit in "the colour of blood" on Wednesday evening for the millions persecuted for their faith around the world.
The iconic home of the British parliament joined Westminster Abbey, Westminster Cathedral, St George's Coptic Orthodox Cathedral and dozens of other churches, mosques, synagogues and landmarks across the UK to be lit red to mark the day.
Muslim, Jewish and Christian leaders took part in the Red Wednesday campaign organised by the Catholic charity Aid to the Church in Need (ACN) to highlight the lack of religious freedom around the world.
A report by the US State Department this year found 76 per cent of the world's population lives with high or very high levels of restriction on religious freedom.
A double decker campaign bus toured London visiting the Imam Khoei Islamic Centre and the Jewish Liberal Synagogue in North London before stopping at St Paul's Cathedral and finishing in Parliament Square.
Gathered outside Westminster Abbey's striking West front bathed in red light, the Syrian Orthodox Patriach of Antioch and All the East, Ignatius Aphrem II, said the sight was a "reminder that martyrdom is still here with us and will always be with us".
He told Christian Today: "Christians and people of other faiths are being persecuted around the world and very little attention is paid to that by the politicians and by the governments.
"It is important that people who are perpetrating violence in the name of religion against people of other faiths are bought to justice and told to stop so others do not do the same thing."
Lord Alton of Liverpool, a Catholic crossbench peer, was behind the campaign to light the Palace of Westminster red. At the end of the day's campaign he said the support had been "extraordinary".
He told Christian Today: "Millions of people are suffering because of their faith. Article 18 [on religious freedom in the Universal Declaration of Human Rights] is breached daily.
"Whether you are North Korean Christian in a gulag or you're an Ahmdi living in Pakistan or Bahá'í living in Iran or a Muslim living in Rohingya state in Burma or an atheist in Saudi Arabia – it all amounts to the same thing. People are being persecuted in the most grievous and horrible ways."
Peace between faiths means a shared commitment to love, truth and human dignity. May Christ give us grace to set an example #RedWednesday— Justin Welby ن (@JustinWelby) 23 November 2016
Outside the Jewish Liberal Synagogue synagogue, John Pontifex, spokesman for ACN, told Christian Today it was crucial that Muslims, Jews and Christians worked together.
"By coming together we do not lose our identity. We actually build our identity because we learn a lot from one another and in many cases our identity is shaped by one another," he said. "This is a sense of homecoming."
He added the day was about saying "enough is enough".
He said: "The violence that is carried out in the name of religion should not be carried out. We need to work together to stop this violence.
"The whole notion of Red Wednesday is such that we are shedding a light on all those who have paid the price for their faith with their blood."