"called on London's Catholic parishes to embrace migrants whatever their legal status ahead of a major Mass in the capital.
Cardinal Cormac Murphy-O'Connor has made the call in the Tablet magazine as he prepares for a Mass for migrant workers at Westminster Cathedral on May 1, the Feast of St Joseph the Worker.
He said: "Illegal immigration is not something the Church can approve of or encourage. But our Gospel mandate is to assist strangers, whoever they are, and meanwhile to urge that the rights of undocumented workers be respected."
The Archbishop is bringing the bishops of London's three Catholic dioceses together for the ceremony next week which is expected to attract more than 2,000 people.
Following the Mass the congregation will stage a rally in the cathedral piazza to launch a new Workers' Association and to urge employers to pay a "living wage" to migrant workers.
The living wage is the necessary minimum for a human standard of living in the capital. The Mayor of London Ken Livingstone has set the the living wage at £6.70 an hour, where the national minimum wage is £5.05.
Trade union and faith leaders, including deputy general-secretary of the TGWU, Jack Dromey; the head of the Muslim Council of Britain, Sir Iqbal Sacranie; and the canon theologian of Westminster Abbey, Nicholas Sagovsky will attend the rally.
The Mass, the first of its kind, is organised with the support of London Citizens, a community-based organisation which includes many Catholic churches as members.
Also attending will be the papal nuncio, Archbishop Faustino Sainz Munoz, and the Orthodox ecumenical patriarch Gregorios.
During the ceremony several parts and readings will be conducted in different languages, including Vietnamese, Polish and Spanish, to reflect the changing face of London's Catholic Church.
In his homily, the Cardinal will tell migrants that "as far as the Catholic Church is concerned, you are Londoners".
Tens of thousands of practising Catholic migrants have arrived in Britain's capital, notably from central and eastern Europe following the accession of the new EU states in May 2004. About 90% of the capital's low-paid jobs are performed by migrants.
The tide of newcomers has buoyed Mass attendance figures in the capital's parishes in recent years and led to higher numbers of new Catholics and priestly vocations.
In his Tablet article, the Cardinal recognises the need for ethnic chaplaincies as "a staging post, a path into the wider Church".
However, he also warns against "two parallel Churches in London: one for Londoners, one for foreigners".
The Archbishop said: "Our Church is Catholic, it is not British or Irish or black. As migrants settle and find work, it is to be hoped that they move into local parishes and there find a warm welcome."
In order better to understand the needs and conditions of migrant workers, the three Dioceses have commissioned research entitled "The Ground of Justice", which is being carried out by the Von Hugel Institute in Cambridge together with London Citizens.
Ground of Justice researchers are busy collecting data through interviews with parish priests and migrants across the capital. The research, which will contain practical suggestions for solidarity with the migrant, is expected to be published in September".
One would have two small observations about this report.
Firstly, increased Mass attendance obviously results in increased collections.
Secondly, migrants should not be regarded as 'Londoners' or 'Americans' in the eyes of the Catholic Church, but as, er, 'Catholics'.