‘I will never sit down with Gerry Adams,” said the founder of the Democratic Unionist Party in 1997. Then, in 2007, Ian Paisley did. Which produced another problem. Where should the two men sit?

Tony Blair’s negotiator, Jonathan Powell, relates that a crucial meeting, which ten years of talks had been building up to, was nearly scuppered by a dispute over where the two men should sit — opposite each other (Paisley’s demand, to show they were still rivals), or next to each other (Adams’s demand, to show that they were equals).

Finally an official had a brilliant idea: a diamond-shaped table. The two men could sit at the apex, both next to each other and opposite each other at the same time. The meeting