The hiring of James Purnell is a smart strategic move by the new Director-General, Tony Hall, which strengthens his own hand by changing the dynamics at the top of  the BBC.

Hall will have seen how isolated and exposed his predecessor George Entwistle was in trying to deal with the fallout from the Jimmy Savile and Lord McAlpine furores, and has given himself an important ally.

At just 42, Purnell brings a youthful counter-balance to the experienced DG, who is 61. His knowledge of the fast-changing technological landscape will be an asset to Hall, as will his connections to the key government department and to Westminster in a period when the BBC must fight to retain its public funding.

The former Culture Secretary is an important player in the arts world, as is Hall, who arrives at the BBC from the Royal Opera House. Purnell was head of corporate planning at the Corporation when Hall was head of current affairs.

Most crucially, this appointment affects the relationship between the BBC executive and its governing body, the BBC Trust. Entwistle was very much the appointee of Lord Patten, the BBC Trust chairman, who as a former head of the Conservative Party enjoys a strong  relationship with the Government which helped him to ride out the Savile crisis while his younger protégé took the hit.

Hall arrives at the BBC next month with a mandate to reform. His position is stronger than that of the political warhorse Lord Patten. Having a former Culture Secretary as a wing-man should mean that he can enjoy a degree of autonomy that the BBC careerist Entwistle never knew.