Some political journalists are like weather vanes – they indicate the direction in which attitudes among the pack and the political class are blowing, and then they rush to harden it into established opinion. Gavin Esler’s interview with Alistair Darling on yesterday's Newsnight, the BBC flagship opinion programme, was more than revealing for what it told us about this process when it comes to Labour's new leader Ed Miliband - it was an outrage. 

Esler asked Darling what lay behind Miliband’s "faltering" start. He didn't say that in the view of some he was faltering and ask if Darling agreed. He simply stated it as a fact. Well, it may be the established opinion of the mediocracy. But it is not a fact. Miliband beat the media's Blairite favorite, drew a decisive line line from Blairism by declaring the Iraq war to be wrong, has done well against Cameron in the Commons, handles interviews with Paxman with ease and is clearly taking his time. This may be a mistake. It isn't "faltering". And does a divided and bruised party really want a trendy 'narrative' just yet? Imagine if David Miliband had won. We'd now be witnessing the collapse of his 'nice guy' project in the light of the Wikileaks revelation that he personally signed off permitting the US to retain cluster bombs as a 'temporary measure' so this could be hidden from  parliament. By asserting his prejudices as reality, Esler is coming close to the Foxisation of Newsnight, doubtless the rest of the BBC will follow.

Then the clincher, supposed proof that Ed Miliband is already "faltering": he says he will keep the 50 per cent higher tax rate on those earning over £150,000 a year?

Obviously a blunder! (Although, oddly nothing faltering about it.)

Well, again this is not a fact it is a Fox. What began as a panicky response to Labour’s loss in 1992 – and focus group reports on marginal voters in marginal constituencies – hardened into the creed according to Tony Blair: income tax is a taboo. It can go down but it must never be raised. In New Labour’s three election manifestos Blair and Brown pledged never to raise it. Now it seems this is the BBC's touchstone for measuring good judgment.

Yet, as Polly Toynbee and David Walker write in The Verdict, this was "a profound error, setting up an imbalance between revenue and spending that will dog the second decade of the century."  It was also, they say, "a political mistake".  They argue that the British Social Attitudes (BSA) series of regular polls show that Thatcherism never persuaded the majority of the public, and that attitudes to tax were ‘mixed’ and ‘malleable’ with majorities in some polls in favour of higher tax to pay for more spending on health, education and benefits.  People were ‘persuadable’ – but, as the latest BSA poll shows, a great deal depends on the willingness of governments to persuade.

It is to be hoped that Miliband won’t falter in this and his Labour colleagues should stop backbiting and learn a little modesty. And Gavin Esler and  Newsnight editors must stop presuming that their prejudices are reality.