Why Britain doesn't play politics with gun tragedy

It was lunchtime on a warm, dull Friday in the West Yorkshire village of Birstall, UK, when locals gathered for an unusual vigil. In the paved marketplace of this small northern town of 15,000, Prime Minister David Cameron stood in silent tribute to fallen colleague Jo Cox, a popular freshman representative of his rival Labour Party, who was gunned down Thursday in the heart of her constituency.

Cameron stood shoulder-to-shoulder with Jeremy Corbyn, the Labour Leader of the Opposition, and with a bitter rival from his own party, Speaker of...