Video report by ITV News correspondent Paul Davies
Pope Francis has said that gay people should not be judged or marginalised and should be integrated into society, but he reaffirmed Church teaching that homosexual acts are a sin.
In a broad-ranging 80-minute conversation with journalists on the plane bringing him back from a week-long visit to Brazil on Sunday night, he also said he could not judge gay priests, an emotive topic that divides Catholic opinion.
Francis stressed the Roman Catholic Church's ban on women priests was definitive, although he would like them to have more leadership roles in administration and pastoral activities.
"If a person is gay and seeks God and has good will, who am I to judge him?," he said in response to questions from journalists.
"The Catechism of the Catholic Church explains this very well. It says they should not be marginalised because of this (orientation) but that they must be integrated into society," he said, speaking in Italian and using the word "gay", instead of "homosexual" which previous pontiffs mainly used.
"The problem is not having this orientation. We must be brothers. The problem is lobbying by this orientation, or lobbies of greedy people, political lobbies, Masonic lobbies, so many lobbies. This is the worst problem," he said.
Richard Lane, from gay rights group Stonewall, said that a change in tone from the Vatican on gay rights was a welcome "small step" but suggested a wider ranging statement condemning the persecution of gay people would be a more significant development.
A Stonewall statement also described as "baffling" the Pope's comments about the "problem" of lobbying from gay rights groups:
The pope arrived back in Rome on Monday after a triumphant tour of Brazil, which climaxed with a huge gathering on Rio de Janeiro's famed Copacabana beach for a Catholic youth festival that organisers said attracted more than 3 million people.