In his new post, Alastair will advise on reputation management and the strategic development of integrated campaigns across media, public affairs and the digital space.

He will also work with Portland CEO Tim Allan to develop and mentor the agency's staff.

Alastair said: "I have had plenty of offers since I left Downing Street to join PR consultancies or go in-house. It was not something I ever thought, to be honest, that I would do. But Tim Allan is nothing if not persistent and over the last few months, I have found myself working with Portland more and more, advising clients and helping develop their bright young staff."

"I have thoroughly enjoyed the chance again to help build a talented team, particularly as Portland includes a good number of friends from my days in the Labour Party and at Number 10. These are people I know to be of the highest calibre and of strong values and commitment to professional standards. It is why, when Tim recently asked whether I might like to formalise my role at Portland, I finally said yes."

He will continue his other work, which includes writing, public speaking, coaching, broadcasting, unpaid political advice, charitable fundraising and awareness campaigns.