Pope Benedict is to meet the prime minister and senior politicians on the third day of his four-day state visit.
As well as seeing David Cameron, the Pope will meet Deputy Prime Minister Nick Clegg and acting Labour leader Harriet Harman.
He will then celebrate Mass at Westminster Cathedral before visiting a home for older people in south London.
The day ends with a prayer vigil in Hyde Park. Opponents of the visit are to march and rally in central London.
During the Mass at Westminster, the Pope will send a message of greeting to the people of Wales, as he is unable to visit them “because of the pressures of time” according to a spokesman.
Afterwards he will greet an invited crowd of 2,500 young people in the Cathedral Piazza outside, who will include a representative from every parish in England and Wales, a contingent from Scotland, and a number of volunteers from Catholic youth organisations.
About 80,000 people are expected to attend the open-air vigil in London’s Hyde Park later.
But there will also be a march on Saturday afternoon organised by the Protest the Pope – and umbrella group opposed to the Pope’s visit – from Hyde Park Corner to Downing Street, where a rally will be held.
On Friday, in his keynote speech to MPs, senior members of British society and religious leaders at Westminster Hall, the Pope warned that religion – and Christianity in particular – is “being marginalised” around the world.
Pope Benedict XVI warned that there were some people who wanted to see “the voice of religion be silenced”.
He returned to the subject in a service at Westminster Abbey, asking Christians to speak out about their faith.
In his speech at Westminster Hall, the Pope called on those in attendance to seek ways to promote faith “at every level of national life”.
He added: “I cannot but voice my concern at the increasing marginalisation of religion, particularly of Christianity, that is taking place in some quarters, even in nations which place a great emphasis on tolerance.
The Pope says that religion is ‘marginalised’ during his speech in Westminster Hall
“There are those who would advocate that the voice of religion be silenced, or at least relegated to the purely private sphere.”
He also expressed concern over arguments that the public celebration of festivals such as Christmas should be discouraged, in the belief it may offend those “of other religions or none”.
Earlier on Friday, the Pope met Archbishop of Canterbury Rowan Williams at Lambeth Palace – a meeting attended by Anglican and Roman Catholic bishops from different parts of the UK.
The Lambeth Palace meeting marked the first time a Pope has met the archbishop at his official residence.
It was viewed as an important event more than 40 years after official talks began about possible reunification of the two churches.
Divisions remain over Roman Catholic opposition to the ordination of women priests, while the Church of England’s General Synod left the way open for appointing women bishops at its meeting in July.
The Vatican angered many supporters of women’s ordination by describing it as a “grave crime” to be dealt with in the same process as sex abuse, though it denied it was equating the two.
Dr Williams said in his opening remarks that the Pope was “most welcome” at Lambeth Palace.
He then praised the pontiff’s “consistent and penetrating analysis of the state of European society”.
Meanwhile, six men remain in custody as counter-terrorism detectives investigate an alleged threat to Pope Benedict XVI’s visit.
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