The pioneering Alpha course which began in one parish in the Church of England nearly four decades ago is now being used in more Catholic than Anglican parishes, according to the Archbishop of Canterbury Justin Welby.

Archbishop Welby revealed the latest phenomenal success of the evangelisation course, with its strong emphasis on the power of the Holy Spirit, after meeting the Pope in Rome where he was accompanied by Rev Nicky Gumbel, vicar of Holy Trinity Brompton.

Speaking to Christopher Lamb for The Tablet, the Catholic weekly, Archbishop Welby said: "Every now and then I just like to remind people that it [Alpha] started in the Church of England," adding that he recently had to convince a French Catholic friend that the course had not originated in France. "We [Catholics and Anglicans] are working additionally on evangelisation, and that illustrates the breadth of the relationship. The Catholic Church is much bigger than us and far more widely extended, but we also bring something to the relationship. Alpha is a gift of the spirit to the church of the world not merely to the Anglican Communion let alone the Church of England."

Gumbel, an old friend of the Archbishop who has close ties with Holy Trinity Brompton in Knightsbridge, the home of Alpha, confirmed the Archbishop's comment on the Catholic uptake of the course.

The Tablet reports that during the Archbishop's two-day visit to Rome he witnessed the work of a street shelter project run by the community of Sant'Egidio, met a victim of human trafficking and also saw a refugee project at the Anglican church, St Paul's-within-the-Walls. Combating human trafficking was a theme of the visit and the Archbishop also met with the Global Freedom Network at the Pontifical Academy of Sciences, an initiative founded by the Australian philanthropist Andrew Forrest that hopes to eradicate modern day slavery by 2020.

The Archbishop has a deep interest in Catholic spirituality. He is oblate of the Anglican Elmore Abbey, Berkshire and has invited a Catholic ecumenical community, Chemin Neuf, to take up residence in Lambeth Palace.

Meanwhile, the charismatic underpinnings of the Alpha course are popular with many in the Catholic renewal movement. Pope Francis recently became the first Pope to attend a charismatic renewal prayer gathering at Rome's Olympic stadium.

"The Pope is clearly charismatic in that one sees the work of the spirit through his ministry and life," the archbishop told The Tablet. He emphasised that he used the word "charismatic" in a broad sense. "I am not naff enough to confine how we define charismatic theologically to someone who speaks in tongues and holds their arms up when you have to say 'hands down to those who are having tea'."

Further initiatives between the two churches could be on the agenda, the Archbishop revealed. The Catholic church still teaches officially that Anglican orders are null and void. Archbishop Welby said: "There are things being discussed, and I'm not going any further than that."

The Alpha course began in 1977 at Holy Trinity and was taken over by Nicky Gumbel in 1990 when he was curate. The course focuses on Christian teachings and beliefs shared by the main churches. Denominations such as Catholics and Baptists with different doctrines to the Anglicans on some matters usually do follow-up courses of their own.

In 1993/4, the first year figures were collected, 25,000 people did an Alpha course in the UK. By 2012 this had grown to nearly 300,000 a year in the UK. Nearly 22.5 million have now done the course in 163 countries worldwide.

Alpha in a Catholic Context is a version of the course especially geared to Catholic parishes. The first Alpha conference for Catholics was in 1996 at the invitation of Cardinal Basil Hume, the late Archbishop of Westminster. It is now running in Catholic parishes in 70 countries. According to the Alpha website, it attracts young people who are asking the question: "Is there more to life than this?"