Matthew Norman: Alan Johnson is just the man for the battle Labour must fight

A week after George Osborne was cheered by imbecilic Tory backbenchers driven to the verge of ejaculation by the most vicious assault on the poor in memory, the Opposition remains marooned in mumbling bemusement. Ed Miliband has done little wrong as leader, and one crucial thing (see below) that was absolutely right.

Yet if Labour suddenly looks paralysed by indecision, that's because it is. In so far as it has any economic policy, as a leaked internal memo admits, it has no substance and little detail. Thus David Cameron swats Ed aside with the most facile of putdowns: if you don't have a plan yourself, shut it you slaaag (I paraphrase marginally).

The source of Ed's current paralysis is easily understood. The urge to wait patiently for the scything of welfare to ignite social unrest and make the Coalition profoundly unpopular must be intense. A full-frontal, tribalist attack on Osborne's deficit reduction plan would make no sense, meanwhile, in the absence of a well-defined alternative, and would dangerously undermine his positioning as a responsible centrist.

For all that, this is no moment for playing it safe. Agnosticism is not an option on the dominant issue of the day. Defensive caution is, in fact, a bigger gamble than taking a risk, because new leaders have very little time to establish the persona that defines their leadership. If this nervous nelliedom continues, he will bury Labour alive in the coffin of irrelevance, and oblige him to rely solely on the implosion of Mr Osborne's calculations that seems a little less likely after yesterday's unexpectedly strong growth figure.

The challenge is to do to the Government's argument what the Tories falsely promised to do with public spending, and take a scalpel to it rather than a machete. Here we come to that crucial thing Ed got right, which was making Alan Johnson his Shadow Chancellor. This was the easy bit. The trickier bit is deploying the languid postie as his scalpel, or rather as the smart bomb targeted on the one specific aspect of the Osborne plan that could yet re-toxify the Tory brand with the radioactive waste of Thatcherite vindictiveness.

It's tricky because what everyone loves about Johnners is the self-parodic detachment he would have to jettison. His gag about rushing out to buy a primer on economics was typically endearing, but wryness has its time and place, and that's not here and now. The tone Johnners needs to find, or synthesise, is the controlled, empathetic fury that would more than neutralise his economic illiteracy. What makes him such an indecently perfect Treasury spokesman is that (dread cliché) narrative of his, and its central relevance to this debate.

Now no one in their right mind would cite Christine O'Donnell as a template for electoral success. The Tea Party candidate is given a 0.00 per cent prospect of winning the Delaware senatorial race on Tuesday by American psephological wizz Nate Silver, and this probably flatters her chances. When she followed that arresting campaign advert opening line, "I'm not a witch", with the freshly minted catchphrase, "I'm you!", it made no sense to those who didn't include midnight trips to satanic altars in their rites of adolescent courtship.

Johnners, on the other hand, could strike a resounding chord with "I'm you!"... or more precisely, with the even catchier: "I'm what this government won't give your children an earthly chance of ever becoming." Under a poisonous housing policy self-evidently designed to drive the poor out of state-subsidised homes in decent urban areas, a 15-year-old today would not be brought up by an elder sister, as he was, in a Battersea flat. He would at best be relocated, or dislocated, to an unfamiliar part of the country in which finding any work would be infinitely more difficult than in London; and at worst taken into care with all the gruesome implications that go with that.

At the age when Messrs Cameron and Osborne were trashing Oxford restaurants under the Bullingdon banner, Johnson was stacking Tesco shelves. While The X Factor is far beneath his purist Mod tastes, he might make the populist point that there must be more reliable escape routes from Tesco drudgery for the talented poor than that pioneered by the show's Mary Byrne now that trade unionism has gone out of vogue.

It is a primary responsibility of a civilised state to enable bright young people to surmount a hideous start. A perfect paradigm of social mobility himself, thanks at least in part to welfare, Johnson needs to do what doesn't come naturally, and get livid about this systemic attack on human potential from silver spoonists without the imagination to empathise one iota with those from backgrounds like his own.

This is not about primitive class warfare, but its polar opposite. It is about aspiration. It is not about enshackling the poor to poverty with infantilising statist patronage, but preserving their freedom from its most spirit-crushing iniquities. It is about clearing a hurdle from their path rather than doubling its height, and doing whatever possible to ensure that a dirt-poor child with a good brain and fierce ambition has at least a shot at reaching a British Cabinet, rather than making a working lifetime of stacking shelves inevitable.

Labour needs to use housing policy to reframe this ideological battle as one between liberation and enslavement, and only Alan Johnson has the popularity and personal story to do that. It is an emotional argument more than an economic one, so he can safely bin the primer and leave the sums to Mr Miliband. He should muscle his way to centre stage, however distasteful he finds the solipsistic self-indulgence involved, and talk incessantly about himself; and why, under Mr Osborne's plan, he might never have escaped the limitations of his childhood.

Oppositions usually flail about in search of a raison d'être in the wake of an electoral disaster, but this one has neither the time nor the need. Its clear purpose must be promoting the social mobility it so shamefully neglected when in power, and its cause protecting the Little Orphan Alans from this odious Daddy Nobucks of a Chancellor. He needs to start scrapping on behalf of his 15-year-old self – and not tomorrow, which after all is always a day away, but today.