Most observers would agree that Yvette Cooper, the shadow home secretary, is a serious person. One newspaper profile last year spoke of her ‘steely determination’. Sir Keir Starmer knew what he was doing when he appointed her to the Home Office brief, the toughest and most unforgiving in Westminster. On Wednesday, while the party leadership was mired in accusations of purging its left wing, Cooper went into bat for Labour’s law and order credentials, promising to ‘take back our town centres from thugs and thieves.