It's not 1997 any more. This shouldn't need saying, but attacks on Jeremy Corbyn such as this from Ian Austin suggests it does. He accuses Corbyn of wanting to turn Labour into "something very different" from its traditional mainstream social democracy.

What this misses is that Labour must reinvent itself, because the economic challenges we face now are very different from those of the 1990s. Take four examples:

1. In the 90s, real interest rates were high: longer-dated index-linked gilt yields were over 3.5% when Labour took power. Such high yields meant that the fiscal arithmetic worked against government borrowing; even modest deficits would have meant an ever-rising debt-GDP ratio. There was therefore a good reason for Labour to be "fiscally responsible". Today, however, real yields are negative so the fiscal arithmetic means deficits are compatible with debt sustainability. And with Bank rate close to the zero bound (whereas it was 6% when Blair was first elected), there's a much stronger case for looser fiscal policy.

2. Labour productivity and investment were growing OK in the 90s. That meant the job of economic policy was largely to keep the show on the road - to offer business a stable policy framework within which confidence to invest and innovate would be maintained. Today, of course, things are very different. Productivity has pretty much flatlined for years, and the share of business investment in GDP was a percentage point lower last year than it was in 1997. This suggests a case for governments to take a more active role to raise productivity and investment.

3. New Labour thought that a stable policy framework was sufficient to ensure macroeconomic stability. We know now that this is not the case and that even with stable policy, capitalism can generate severe crises.

4. In the 90s, the inequality that bothered Labour was the 90/10 ratio. It was reasonable to ameliorate this through tax credits, a minimum wage and university expansion. Today, though, even once middle-class people are struggling, especially those too young to have bought a house. Instead, the inequality that matters most is the share of incomes going to the very top. In the 90s, this was just over 10%, but rising, whilst today it is over 14%. It's plausible that this inequality - and the inequality of power that generates it - has contributed to our poor economic performance.

Even the most narrow-minded technocrat must therefore see that our changed economy requires a changed response (and in fact many technocrats in the Bank of England or IMF do see this). As Joe Guinan and Martin O'Neill write:

If we are serious about addressing real economic challenges then we need a different set of institutions and arrangements capable of producing sustainable, lasting, and more democratic outcomes.

Such arrangements mean not just looser fiscal policy but, as they say, measures to increase investment and oppose managerialism, such as worker coops. Measures such as more public ownership, a state investment bank and more co-ops are things any European would recognise as social democratic. Yes, it's a different from of social democracy from New Labour's. But a different economy requires different policies.

This is not to say that Corbynism is perfect. Far from it. I'm not keen on its student politics anti-imperialist posturing,and have my doubts about its economic plans: I'm not sure whether it can raise billions more in corporate taxes; its desire for more coops requires tons of detailed work; and I'd like to see more acknowledgement that there is still a big role for markets and entrepreneurship to play.

My gripe with Labour's centrists, however, is that they seem oblivious even to the basic fact of capitalist stagnation and the challenges it poses: Austin writes as if a decade of falling real wages hadn't happened.

And herein lies a paradox. Corbyn and McDonnell are, from this perspective, the true heirs to Blair. They recognise - as Blair did in the 1990s - that a new economy requires a new form of social democracy. And their critics, like Blair's critics in the 90s, seem unaware of this fact.