Jean-Christopher Gray has been appointed as The Treasury's head of press and the Chancellor's principal spokesman, having previously headed up the Treasury's EU finances team.
Gray was also private secretary to Gordon Brown when he was chancellor. He has not previously held a press-facing role.
One senior Whitehall comms source said: 'The Treasury has a history of promoting internally, but it's a lot more visible at the moment. They might think they walk on water, but I don't think others do. Maybe this would have been a good time to cast the net wider.'
Another former Whitehall director of comms added: 'If he's been in private office he'll know about the media-sensitive side of policy, and will probably be seen as a safe pair of hands because he'll know his stuff on policy.'
Gray will take over from head of comms Steve Field as the Chancellor's spokesperson. Field has been promoted to the role of director of strategy and communications.