Thousands have marched in London to protest against the Pope's visit.
Organisers of the Protest the Pope event said they wanted to highlight his stance on controversial subjects, including the ordination of women.
Sex abuse and Catholic opposition to contraception have also been criticised.
Organisers of the protest say 20,000 people took part in the rally; however, police say they are unable to confirm this figure.
The march proceeded from Hyde Park Corner through central London to Whitehall where a rally was held with speakers including gay rights activist Peter Tatchell.
The event took place as Catholics gathered in Hyde Park for an evening prayer vigil led by the Pope.
Among the protesters was comedian Al Murray.
He said: "Like a lot of people I am a perplexed that it is a state visit.
"The Pope's opposition to condoms kills people. It is all very well him lecturing us on morals but he should look at his own organisation's view."
Speakers at the rally included the human rights lawyer Geoffrey Robertson and atheist scientist and author of The God Delusion, Richard Dawkins.
At the rally, Mr Robertson said: "We are here today to celebrate our faith in liberty of conscience; our faith in equality; our faith in human rights.
Of the Pope he said: "He's been met with the most utter, exquisite, grovelling politeness and with that somehow we are in an uncivilised third world country.
"What is civilised about demeaning the women, demonising homosexuals, wishing that IVF children had never been born?... our only crime has been silence."
On its website, Protest The Pope says it opposes Pope Benedict's state visit because "he is going to use (it) to tell us how we all should live and to interfere in our laws. No other head of state would be allowed to do this".
In particular, the movement criticises the Vatican for:
- "opposing the distribution of condoms and so increasing large families in poor countries and the spread of Aids"
- "promoting segregated education"
- "denying abortion to even the most vulnerable women"
- "opposing Lesbian, Gay, Bisexual and Transgender rights, including universal decriminalisation of homosexuality"
- "failing to address the many cases of abuse of children within its own organisation"
While accepting Pope Benedict's right to visit the UK and to address his supporters, the Protest The Pope campaign opposes the fact that it is, in part, financed by UK taxpayers.
'Critical of policies'
Mr Tatchell told the BBC News Channel: "We profoundly disagree with the Pope's opposition to women's rights, gay equality and the use of condoms to prevent the spread of HIV.
"This is not an attack on Catholic people or the Catholic faith. We are critical of certain policies of the Pope.
"When he says no woman is fit to be a priest, that's an insult to the whole of female humanity.
"When he says a husband must not use a condom to protect his wife from infection - even if he has HIV - that's irresponsible.
"And when he says that all gay people possess a tendency towards evil, that flies in the face of the Christian gospel of love and compassion.
"We know that many Catholics share our concerns. Only 5% of Catholics in this country agree with the Pope's ban on contraception. Only 11% of Catholics think that homosexuality is morally wrong.
"So there is a great depth of Catholic opinion which is in disagreement with this Pope and we support those Catholic people."
'Accept traditional values'
In response to the Pope's public apology over child abuse within the Catholic Church made during a Mass at Westminster Cathedral, Mr Tatchell said: "The Pope keeps on apologising for the failings of everyone but himself."
Ahead of the march, protesters heard from a victim of clerical sex abuse.
Sue Cox, 63, from Gaydon, Warwickshire, told the gathered crowds that the Pope's visit was "egotistical, arrogant and selfish".
She said: "How dare he suggest that secularism does not accept or tolerate traditional values?"
She added that her own experience from the Catholic Church was "pain, anger, fear, terror, disgust, lies, shame, violence, sneering, disdain, and disempowerment."
John Hide, one of the people attending the protest, told BBC News: "I am very much against the taxpayer having to pay for the Pope's visit.
"I have also just found out that the Queen has to wear black when she meets the Pope as a sign of deference. That is incredible."
Father Christopher Jamieson, a Benedictine monk and the director of the Catholic Church's National Office for Vocation, said the protest was part of living in a democratic country.
He said people had every right to protest but "we feel he has been received very fairly and very warmly.
"It's been a great affirmation not only for the Holy Father and church, but also for the country, that its political system is so capable of welcoming into the political platform a religious voice whose voice is not always welcomed to all parts of society.
"That too is a great expression of democracy."