Buildings are being floodlit red on Wednesday to remember millions of Christians around the world being persecuted for their faith.
Red Wednesday is an annual initiative of Catholic charity Aid to the Church in Need (ACN) and this year's event will remember persecuted Christian children in particular.
In a video message, Cardinal Vincent Nichols appealed to all people to get involved, and said the most important way they could support persecuted Christians was "in your prayers".
"Let's not forget those who in the world today directly suffer with Christ – the persecution that he bore on the Cross and they bear in their lives – especially the children," he said.
"Let them not be forgotten. Let them be in the focus of our hearts and our prayers."
In the run-up to Red Wednesday, ACN invited people to sign an open letter to Foreign Secretary David Lammy asking that the government commit more foreign aid in support of Christians and other religious minorities being persecuted for their faith.
"ACN research consistently shows that oppression has intensified, and impunity against perpetrators has grown," the letter says.
"This persecution included extreme violations of Article 18 of the UN Universal Declaration of Human Rights; the right to freedom of thought, conscience, and religion."
A special Red Wednesday Mass will be held at Brompton Oratory in London joined by Archbishop Linus Neli of Imphal, India, and Monsignor Michael Nazir-Ali, who fled to Britain from Pakistan in the Eighties due to persecution.
During the evening, ACN will present its Courage to be Christian Award to a Christian who has suffered for their faith.
In addition to the UK, over 300 events to mark Red Wednesday will take place around the world in Australia, Canada, Chile, Columbia, France, Germany, Italy, the Philippines, Slovakia, Spain, Switzerland and the US.
Supporters of Red Wednesday include Lord Alton who said the persecution of Christians "remains a significant challenge worldwide".
"Today, we especially raise the suffering experienced by the largest group of people persecuted for their faith worldwide," he said.
A day before Red Wednesday, he received a written reply from Lord Collins of Highbury on behalf of the government to a question he submitted asking what action is being taken to encourage respect for religious freedom in China.
The written response said that the UK government has repeatedly raised the issue with China.
"This government stands firm on human rights, including the right to freedom of religion or belief," said Lord Collins.
"The Foreign Secretary raised human rights in every meeting with his Chinese counterpart Foreign Minister Wang Yi, including during his recent visit to China on 18 October.
"More broadly, this government will champion freedom of religion or belief for all internationally. We will work to uphold the right to freedom of religion or belief through our positions at the UN, G7 and other multilateral fora and through bilateral engagement."
