A flannel shirt is an unsung wardrobe hero. Hardy and warm, it comes into its own at this time of year. Just don’t confuse it with a cotton checked shirt: flannel means it is brushed wool or cotton, making it soft to the touch and unlikely to crease. Wear with denim, boots and an overcoat for off-duty style; or promote it from layering piece to overshirt. Here are the market leaders right now…