It was a moment pregnant with symbolism, but one that remained closed to the public and was initially intended to not even be photographed: a senior Irish republican shaking the hand of the British Queen.

The deputy first minister of Northern Ireland shaking the hand of the monarch who remains head of state of Northern Ireland would normally be a fairly mundane affair. But the office is held by Martin McGuinness – not just a Sinn Féin politician, but also a leader of the Irish Republican Army, which fought a three-decade bloody civil conflict against British forces.

Given who he is, the handshake is being hailed as the final major act of the Irish peace process....