Senator Elizabeth Warren has urged regulators to block Capital One’s $35bn takeover of Discover Financial, arguing that combining two of the US’s largest credit card companies would harm consumers and challenge financial stability.The blockbuster deal would inevitably lead to higher costs and fees for cardholders, according to the leftwing senator.Richard Fairbank, chairman and chief executive of Capital One, has claimed the planned acquisition amounts to “a singular opportunity to bring together two very s ...