In the aftermath of the Westminster Bridge terror attack this year a woman in blue coat was photographed tenderly cradling the head of a man who had been struck by the car of terrorist Khalid Masood.

Crouching over him, her hands covered in blood, she gently tended to his wounds and whispered reassurances as they waited for paramedics to arrive. To one side his shoes lay neatly on the pavement, belying the terrible force that had prised them from his feet. In his unseen hand he clutched a postcard of The Queen.

In the confusion that followed it was unclear whether the pair knew each other, or if a kind-hearted stranger had stopped to help the stricken man.