Leading article: A threat to Labour's credibility

Alan Johnson's inability to tell a Sky News interviewer over the weekend the rate of national insurance paid by employers was merely the latest in a string of unconvincing performances. Before taking up the job of shadow Chancellor, Mr Johnson seemed unsure whether VAT was levied on food. And since being appointed to his post in October, he has sent out confusing messages over how quickly Labour would cut the deficit and the party's attitude towards a graduate tax. It is unsurprising therefore that, even within his party, some are beginning to mutter about his suitability for the post.

Ed Miliband, Labour's leader, defended Mr Johnson at a press conference yesterday. But over the weekend he will have again wondered whether he chose the wrong man. Mr Johnson was selected as shadow Chancellor for two reasons, neither of which relate to his grasp of economics. First, he is not Ed Balls, the bruising shadow Home Secretary, whom Mr Miliband feared would be difficult to control if given responsibility for economic policy. And second, Mr Johnson's common touch, born of a working-class upbringing and easy manner, might make a flattering contrast with the Bullingdon demeanour of George Osborne, especially in a time of austerity.

Both those arguments fall apart if the chosen candidate is not seen to be up to the job. It is too soon to make that claim confidently, of course, and his latest gaffe is not proof of incompetence. But in the age of the internet and 24-hour news, perceptions matter more than ever, and Mr Johnson is creating negative impressions of his party.

Gordon Brown worked tirelessly between 1992 – when he became shadow Chancellor – until Labour's election in 1997 to restore his party's credibility in economic affairs, which had been so damaged by the collapse of the Callaghan government and Labour's missteps in the 1980s. Mr Brown recognised very early on that economic credibility takes years to gain but can be thrown away in an instant. That is a lesson Mr Johnson would do well to learn. A talented politician who could be a major asset to Labour through this Parliament, he needs to get a grip.