Exclusive: Head of trade union backs energy secretary to replace Rachel Reeves, but two other big unions are opposed

The boss of Britain’s biggest trade union has endorsed Ed Miliband for chancellor, as the race to take over the Treasury under a potential Andy Burnham government intensifies.

Andrea Egan, the general secretary of Unison, has backed the energy secretary, who is one of two frontrunners to replace Rachel Reeves in No 11, but who is being opposed by two other large unions – GMB and Unite.