Will McDonnell's determination to shift power to the state and unions be a vote winner or loser? Robert Peston asks
In the next election, as in the last one, McDonnellism will prove a serious challenge to the Tories.
John McDonnell, as chancellor, confirmed - if such were needed - that in government, he and Jeremy Corbyn would make a full frontal attack on 40 years of economic and industrial orthodoxy, the precepts that markets know best and that our prosperity depends on trusting the private sector.
During the first 30 years, this orthodoxy may have delivered relatively steady income growth for the economy as a whole.
But over the full 40 years, we've seen the greatest shift in history between the share of national income that accrues to workers and what is taken by the owners and providers of capital.
And as a corollary, at the start of those four decades of the Thatcher and Blair consensus, the gap between rich and poor dramatically widened, and has never been reversed to any serious extent, while living standards for the majority have stagnated since the 2008 crash.
The cake may have been enlarged, but workers' share of the cake shrank.
So what McDonnell wants to do is empower workers, via unions, to recoup much of that lost share of income via their pressure on employers.
Also he would dramatically intervene in the functioning of the economy to directly transfer significant income and wealth to employees.
All of which will be hated by those who invest in businesses and manage them.
And in a global economy such interventionism may damage the ability of the UK to attract talented people and investment.
But politically the inevitable attacks that would come from the Tory Party would probably help Labour in a coming general election - because they would highlight pledges from the Shadow Chancellor that may well appeal to millions.
For example, McDonnell said today he wants the working week to fall to roughly four days on average over ten years, including creating a new commission that would force employers to increase minimum statutory paid holidays every year, along the lines of how the Low Pay Commission sets what it deems to be a minimum or living wage that the nation can afford.
Company bosses will hate this costly interference in how they run their businesses - and their profit margins will be squeezed by the corresponding rise in the price of people.
But which senior Tory will be brave enough to say in an election that it would be outrageous for British people to have longer holidays?
Similarly, McDonnell wants to force businesses to negotiate sector-wide pay deals with unions whose rights to take industrial action would be enhanced.
Again this will be hated by bosses.
But if the Tories shout and scream about this, they may well be repeating the mistake they made in the 2017 general election - when they learned that their shouted attack on Labour's plans to nationalise the railways and the energy sector did Labour an enormous favour, because it turned out even Tory supporters thought the state would do a better job than the private sector in running the trains and keeping down the cost of gas and electricity.
The point is that trade union barons may have been feared as over-mighty and destructive to wealth creation in the 1970s.
They may not exactly be loved today.
But today it is those who own and run Top Shop or Thomas Cook or Southern Railways who have a worse public reputation.
Similarly, McDonnell wants to put a cap on private sector rents - which may well distort the market in a way that reduces the supply of accommodation, but will be seen by most as tackling the scandalous shortage of decent and affordable rentable housing.
Then there's the plan to give employees a 10% stake in their respective businesses over 10 years. Investors and managers are wincing.
But giving people a stake in companies that have conspicuously transferred fortunes to managers and investors over decades is unlikely to be a vote loser.
There are a ton of other policies that conventional politicians since 1979 would regard as toxic, such as borrowing £500bn over ten years for green and mainstream investment, or increasing taxes by £6bn a year to fund personal care for the elderly, or offering £2.5m interest free loans for the purchase of new electric cars, etc etc etc.
What McDonnell wants to engineer is the biggest shift in power towards the state and trade unions since the Labour election victory of 1945 - which in and of itself would have been a guarantee of electoral humiliation in pretty much every election since 1979.
Maybe it will flop again.
Maybe what Labour decries as "neoliberalism" really is now hardwired into the voting intentions of the majority and McDonnell is writing another one of those notorious political suicide notes.
But here in Brighton it doesn't feel that way. If Johnson has worked out that millions want to end the Brexit paralysis, McDonnell is tapping into a national yearning for an end to the politics of fatalism and despair.
If I were Johnson, I would not assume Labour will be a pushover in the coming election.