The corporate tax rate should come down: so says the City, the Lord Mayor, the CBI, the Conservatives and even Gordon Brown. Last month the prime minister told companies: “Our aim, I tell you, is to reduce corporation tax even further when we can afford to do so.”

But the arguments about the benefits of cutting the corporate rate are complex – and difficult to sell to voters. Philip Hammond, the Conservative Treasury spokesman, says: “In recent years, it has been challenging to make the case for lower corporation taxation. Big corporate profits have made it difficult to explain to the public why big companies need more relief.”