There might be fewer of them in Britain – but the Christians that do still exist are doing more good in society.

A new report shows that while overall numbers of Christians have declined, they have become more socially active.

Doing Good: A Future for Christianity in the 21st Century, by Nick Spencer for the religion think tank Theos shows the huge social contriubution that Christians are making to society, motivated by their faith.

They are active throughout the country in volunteering to help with debt advice, homeless charities, mum and toddlers' groups, food banks and Street Pastors.

The report demolishes the secular myth that the demise of Christianity is imminent.

It does admit there has been a decline however.

In 2006 when Theos was founded, there were about 4.5 million people Sunday worshippers in the UK. Just ten years later this has fallen by 300,000 and is now down to about 4.2 million, consisting of one million Anglicans, one million Catholics and 2.2 million others.

The Archbishop of Canterbury Justin Welby, in the foreword, says: "While critics prophesy its imminent demise – as critics have done for several hundred years – Christians across the country are doing what they, too, have done for many hundreds of years: worship, pray, witness, serve."

There is nothing strange about this, he says.

Writing with the Archbishop of Westminster Cardinal Vincent Nichols, he continues: "What is strange – or at least worthy of greater notice than it usually receives – is that the breadth, depth and intensity of this Christian service is deepening.

"From personal debt advice to marriage counselling, from foodbanks to street pastors, from rehabilitation to reconciliation, the Church and Christian charities across the country are rolling up their sleeves, struggling on behalf of human dignity, pursuing the common good – and doing it all in the name of Jesus Christ."

Britain's two leading churchmen assert that politicians and commentators across the political spectrum are realising that a good society needs people dedicated to service.

Spencer said: "Christianity in 21st Century Britain is liable to be smaller but more activist. Fewer people will naturally call themselves 'Christian' but those that do will do more about it.

"This is something that should be welcomed, not least as the evidence strongly suggests that religious worship and social action are strongly correlated with well-being and good mental health."