Until late this morning, Alan Johnson had never been mentioned as a possible shadow chancellor. The widspread assumption was that the post would go to either Yvette Cooper or Ed Balls, Labour's two most economically literate figures, who finished first and third respectively in the shadow cabinet elections. Miliband's decision to hand the post to Johnson, a Labour veteran whose time many felt had passed, has taken almost everyone by surprise.

But Johnson, who the Tories have often described as the Labour politician they fear the most, may yet prove a canny appointment. From a Labour perspective, the affable former postie provides the perfect contrast with the man formally known as Gideon George Osborne. And the appointment of a key David Miliband ally will do much to bolster the Labour leader's pluralist credentials. Derided by some as a left-wing factionalist, Ed Miliband has shown that he can reach out to his brother's supporters.

The appointment also suggests that Miliband's position on the deficit may be closer to the original Darling plan than previously thought. Johnson has consistently defended the election pledge to halve the deficit by 2014 and has warned against an overtly anti-cuts strategy. It's notable that since his election as leader, Miliband has emphasised his desire to "do more from taxation", rather than any dramatic slowing of the deficit reduction plan.

The risk of a Balls appointment was always that the Tories would seize yet another opportunity to exploit divisions between a Labour leader and his (shadow) chancellor. And beyond the economics, Balls and Miliband's personal relationship is notoriously poor, as was demonstrated at the New Statesman Labour leadership hustings in June. After one particularly verbose answer from Balls, Miliband quipped, "It's like being back in the Treasury." (Both were advisers to Brown in his days as chancellor.) To which Balls humorlessly replied, "Tell us the answer then, Ed, like you normally do."

In any case, Balls should relish the opportunity to shadow the Home Office. Like David Davis in the past, Labour's toughest streetfighter now has the chance to claim a series of ministerial scalps from a notoriously vulnerable department.

I can't help but feel that Yvette Cooper -- articulate, cerebral, popular -- was the woman for the job, but time is on her side. Miliband's surprise appointment will have Tory strategists scurrying back to the drawing board tonight.