There was a time when Roman Catholics in Britain shied away from the search for Christian unity, preferring to take shelter behind self-contained, complacent walls. Sooner or later other Christians would come round to the one true Church, it was believed.

Catholics who took seriously the search for Christian unity were dismissed by others as “ecumaniacs”.

But then came the Second Vatican Council, which made clear that the search for Christian unity is an integral part of what it means to believe in Jesus.

Catholics woke up to the scandal of division among Christians, which undermines their witness to the world, because in Christ there is only one Body.

Most of the Christian Churches have shed their proud self-reliance. Pope John Paul II has likened the division between the Catholics and the Orthodox to a person breathing with only one lung.

Yet most Catholics still do not think of the search for Christian unity as an essential part of their life and witness.

A Westminster diocese workshop in mid-March organised as part of the At Your Word, Lord renewal programme aims to change that idea.

At “Cornerstones of Christian Unity”, hundreds of Catholic parishioners, accompanied by friends from other Churches, will hear how Christians are all in it together now.

Fr Mark Woodruff, a priest of the diocese who is one of the speakers, will tell them how the search for Christian unity is really a search for Christ - because in Christ all is unity.

This idea, says Fr Woodruff, is in the very DNA of the Catholic Church.

“I want to communicate to people that the search for Christian unity is not an add-on to Catholic belief,” he says. “It is the driving force of what it is trying to achieve in the whole of humanity.”

“We are one Body in Christ,” he continues. “The fact of our separation does not mean we have to go it alone.”

Fr Woodruff believes that is now the task of ordinary Christians to stop resisting what he calls the “grace of unity”.

“We need now to experience the ‘ecumenism of life’, the meaning of what it is to be fellow baptised Christians,” he says.

He believes the At Your Word, Lord faith-sharing groups which since 2003 have met across the diocese have played a vital role in encouraging ordinary Catholics to be more courageous in their faith.

The “heart-to-heart” model of faith-sharing is precisely the kind which will foster greater communion both between Catholics and between Catholics and other Christians, Fr Woodruff believes.

All across the diocese, thousands of Catholics have been inviting members of other Churches to join their parish-based faith-sharing groups in what is probably the greatest experiment in mass ecumenism ever seen in Britain.

The walls of separation, it is famously said, do not reach to heaven – an idea that Westminster diocese is taking firmly to heart.