When presidents and prime ministers worry about what kind of art to hang on their walls – Barack Obama has hung African-American paintings but also opted for some fairly esoteric modern works – we get a sense of the power politics attaches to the arts.

But just how political is art? Or should it be? I ask this in the week the British Council marks 75 years of bringing UK culture to the world – and the world's culture to the UK. When the council tours the arts overseas, as it did by taking Bridget Riley behind the Iron Curtain in Czechoslovakia in 1971 and more recently sending Gregory Burke's Black Watch, a searing play about the Scottish Black Watch regiment's tour in Iraq, to New York – we can hardly help but ask what role the arts should play or are playing here?

The trouble with cultural diplomacy – don't get me wrong, I like cultural diplomacy – is that it is redundant. Culture is diplomacy. Why? Because the medium in which the arts swim is not really words or deeds but imagination. Which is to say, cultural diplomacy cannot pretend to change how countries do business and probably should not even try. When asked whether his novels contained a message, Nabakov replied in terms cultural diplomats should emulate: "No, I am not a postman".

Sending the Boston Symphony Orchestra to North Korea can no more alter North Korea's position on nuclear weapons than sending Black Watch to New York changed President Bush's position on American engagement in the Iraq war. So while the British Council did both the right thing and the brave thing in exporting Black Watch, it did not do this as an endorsement of official policy. It did so knowing that the values of art need to be allowed to speak on their own terms.

The truth is that democracy needs the art more than the art needs democracy. We need it to exhibit our freedom, to provoke our imagination, to contradict our narcissism, and to redeem our otherness. It belongs at the centre of democracy – and can even embellish diplomacy – but neither as the voice of the patriot nor as the cry of the protester, but at best as the emblem of what democrats aspire to be. That is more than enough.

Taken from a lecture to mark the 75th anniversary of the British Council; www.britishcouncil.org; www.benjaminbarber.com