"We must face the fact that in America, the church is still the most segregated major institution... At 11:00 on Sunday morning when we stand and sing and Christ has no east or west, we stand at the most segregated hour in this nation."

Martin Luther King's prophetic words were uttered in the heat of the battle for Civil Rights in the US in the 1960s. Sadly, they still ring true today. Across America, the racial divide has yet to be healed. Though we in the UK don't have a problem on the same scale, there is still division in our society, and tragically, in our churches.

What some Christians won't realise is that it wasn't inevitable. The response of many white British Christians to immigrants from the Africa and the Caribbean sadly ensured that we have a segregated Church in the 21^st Century. This week, the Archbishop of Canterbury described this as, "the single biggest failure of the Church of England over the last 40 or 50 years." Most Rev Justin Welby went on to suggest that it has had a knock on effect for communities across England, "in terms of how we've dealt with integration – appalling and a great cause of shame to us and to me."

This might seem like an exaggeration, but when the history of the Church and the UK over the last 50 years is examined, it's hard to reach any other conclusion.

When the Windrush arrived in 1948 carrying over 400 Jamaicans to a new life in the UK, a majority of British people were Anglicans. Two years later, in 1950, 67.3 per cent of British babies had an Anglican baptism. While that figure isn't representative of the number who regularly attended church, England (and the rest of the UK) was legally, culturally, institutionally, and to a certain extent ethically, a Christian country.

Into that context the first generations of post-war immigrants arrived. Many of them were not only Christians, but Anglicans. They came from former colonies that had strong Christian presence and thriving Anglican churches. By 1971, the number of Jamaicans in the UK, for example, was 171,000. By then, though, the tragedy had already happened.

The African and Caribbean immigrants who arrived to help revive the moribund British economy were members of Anglican churches, as well as Methodist, Baptist, Adventist and Holiness denominations. When they arrived here and sought a church home, many were left cold by the experience. As Dr Joe Aldred from Churches Together in England recounts, white people weren't interested in welcoming them. "All the signs are that the reason for White disinterest was quite simply the dark pigmentation of the new migrants," he says. "From early on, Black people in the post Windrush era, graphically describe from personal experience... anywhere they cared to look, their reception was as cold as the winter weather they had to get accustomed to. [Black church pioneer] Io Smith complains, 'I was looking for love and warmth and encouragement. I believed that the first place I would find that was in the Church, but it wasn't there'."

Many immigrants were the victims of outright racism in accommodation, transport and employment. If they hoped for a different story when it came to church, sadly, their expectations were often thwarted. Historian Marjorie Morgan tells the painful story of rejection or indifference from White churches. "When many Caribbean migrants started their weekly presence in the majority white churches it quickly became a negative experience of repeated rejection for them. It was the one place where they believed they would be safe from discrimination – they were, nevertheless, persistently disappointed."

She goes on to describe the reality of life as a migrant believer trying to join a white church: "The long established worship spaces in the UK were not readily inclusive of the Caribbean Christians in the early 1960s... Within those environments where the vicars welcomed the migrant worshippers, there was an immediate falling away of the regular white congregation. This lack of integration within the spiritual world in their new home confirmed the complete separation of identity for the migrant black British Caribbean from that of the indigenous white British population."

It is no wonder that in 1999, the Church was accused by one of its own bishops of having "the expectation of the historic, white, educated, elite English norm," while in 2014 the Bishop of Chelmsford, Rt Rev Stephen Cottrell said there remained some elements of racism within the Church.

This is clearly a sad state of affairs. There are numerous reasons the Archbishop is correct to say that the failure to welcome sisters and brothers in Christ in the 1950s and 1960s was a tragedy.

There is a huge cost to such a lack of unity. Not only were the migrants themselves undoubtedly hurt by the unwelcoming spirit, it presented a terrible witness to the rest of the country. A chance to be at the vanguard of racial justice, inclusion and radical welcome across difference was lost. The chance to show that in Christ there is neither Jew nor Greek, White British nor Jamaican, was gone.

Not only did we present a bad witness, but the Church itself was deeply damaged. Both the indigenous church and the immigrant Christians lost out. While the Church of England was in the midst of decades of decline, how much vitality could have been injected by those faithful worshippers from Africa and the Caribbean?

Lack of unity among Christians creates a shameful waste of energy and resources. While some Anglican congregations struggle to maintain their buildings with dwindling numbers, some black majority churches are bursting at the seams and desperate for new premises. This absurd situation could have been avoided. On top of this, the narrative of decline which is popular in the media would have been challenged, if the official figures of attendance at Anglican services (still something which the media obsess over) had been representative of a much broader section of society.

Many churches in big towns and cities in the UK do now have some racial diversity. But this doesn't mean that institutional racism is over. We may have a black Archbishop of York but he has been among the many criticising the slow pace of change of attitudes within the CofE.

There are many congregations in big cities which do have diversity. I've visited plenty of Anglican churches which did (sometimes belatedly) get round to welcoming their neighbours of African and Caribbean heritage. The Church did finally begin to take the issue seriously with initiatives aiming for more diverse leaders and directly challenging racist political movements such as the BNP.

Yet much of the damage has been done and Sunday morning remains one of the most segregated hours of the week. With the Archbishop himself clearly recognizing the depth of the problems and the process of reform and renewal of the Church of England well under way, we can now hope and pray that our churches can reconcile and work together in unity for the good of their cities and for the Kingdom.

Follow Andy Walton on Twitter @waltonandy