A new book on how faith influences politicians, The Mighty and the Almighty, edited by Nick Spencer of the Theos think-tank, is out today.

Chapters cover such figures as Tony Blair, Gordon Brown, George W Bush, Bill Clinton, Barack Obama, Nelson Mandela, Theresa May, Angela Merkel, Vladimir Putin, Ronald Reagan, Margaret Thatcher and Donald Trump.

As the book's introduction explains: 'The purpose of The Mighty and the Almighty is not to discuss nice Christian politicians, or those politicians we would like to be Christian, or those Christian politicians with whom we agree (who, after all, is the 'we' here?). Rather it is intended to look at leading politicians – meaning those who have sat in the highest office – who have claimed some Christian faith, and to explore how they have squared the two; how, in effect, the Mighty (or at least those who professed a belief in him) have dealt with the Almighty when in office.'

But there is an important category distinction here. As Spencer tells Christian Today: 'There are some politicians for whom the faith shaped politics, and others for whom you can be more confident politics are shaping faith – [Donald] Trump is a great example of that. For the majority of politicians it is much messier and only very rarely, if ever, acts in a command and control way.'

An explicit 'hook' for the book is the famous – now clichéd – line by Tony Blair's communications chief Alastair Campbell to an American interviewer: 'We don't do God'.

As Campbell explained to Christian Today last year: 'Now, maybe the reason [the phrase] has become one of those things is because people are aware that Tony is a believer and I'm not. And also people are aware, not least through the diaries, that I always argued against Tony talking about it.

'Now, I think there is an argument to be had about that. And I do think that actually we're very different to America. I think in America politicians have to do "God bless America", they have to be seen coming down the steps of churches on a fairly regular basis, clutching the Bible. I think in Britain it's very, very different. So my view was always the public don't like it.'

As it happens, Blair did in fact speak about his faith while in office, as well as after when he went so far as to set up the Tony Blair Faith Foundation. At Easter 1996, to Campbell's dismay, the then Labour leader of the Opposition wrote in the Sunday Telegraph: 'For a politician, [faith]... means that you see the need for change around you and you accept your duty to do something. Christian belief means you cannot detach yourself from the world around you.' Then in this interview with Jeremy Paxman, a youthful Blair began by saying he didn't like to 'make a big thing of it'. But he went on to say: 'Of course, I'm a person...with a character and part of my character is what I believe in and part of my beliefs is a religious conviction.'

Nonetheless, Spencer agrees with Campbell that British politicians have little to gain by 'doing God'.

'I think it is actually more important than how you do God is where you do God,' he says. 'In those political cultures where you can make political capital out of doing God – places like America and Russia – we should be rightly sceptical. But in places where there is very little political capital to be made – the UK, France, Germany, Australia – we need to be less sceptical than we are.'

By this logic, we need to take at face value the quiet but determined faith, for example, of Theresa May, the current Prime Minister, and even that of Margaret Thatcher before her, not to mention David Cameron and Michael Gove.

After all, who are we to judge what goes on inside the consciences of individuals – even the 'mighty' - and the nature of their personal relationship with God, even if their politics – to us – appear antithetical to the values espoused by Jesus?

For however much we may want them to, surely no political party or agenda anywhere in the world can claim a monopoly on the Christian faith.

Which, in turn, is what makes this book such an interesting idea, charting as it does the attempts, however faltering, by politicians to map their private faith onto their public politics.