It’s a funny thing, standing up and saying Britain is a Christian nation. (Even if you immediately qualify it by saying atheists are moral and other religions are valid too.)
It smacks of dog whistle politics, a statement made because of what it covertly implies rather than from any overt meaning. (“We’re traditional. Support us.”) Often those making the claim want certain policies they believe to be Christian implemented, or not implemented, just because they say so.
As a self declared Christian nation, we supported slavery, torture, invading other countries and running them for our profit, exterminations of less advanced people, arranged marriages, and beating women and children with sticks.
Some Christians would judge how Christian we are as a country by how we treat the poor, sick, and desperate. Some would consider any war or armed force as unchristian. For some overturning dictators by force is noble. Banning Sunday trading, the serving of alcohol, or any sexual content at all in newspapers would be Christian, for some people. The Puritans banned Christmas. Some groups feel Christians should not be sullied by hard practical decisions, and stay out of politics; some don’t look to long term solutions; while to others still, to be a Christian is to seek to mend the world and grapple with the dirty business of making things happen.
The difficulty is that following Jesus subverts the world’s certainties for individuals, and even more so, he undermines our political systems. His sayings are not weighed for long term, best good of the greatest number, practical politics. They aim to shock us with the extraordinary grace of walking the extra mile. Turn the other cheek. Give all you have to the poor. Look first to the plank in your own eye. Do good by stealth.
In short, Jesus is a very odd chap to follow if you want to run a business as usual world spanning empire, or even a second order power with military pretensions.
Every politician should say what beliefs and values drive them, the public forums should allow us to hear and judge accordingly. Attempts to shut religious arguments out of the public sphere, or to declare issues off limits, are totalitarian.
I guess like many I will judge people more by how they act on the metaphysics they claim to act by.