Of all the people Mr Corbyn could have chosen to appoint as his most senior colleague, few could have been more divisive and uncompromising than John McDonnell.

He is a Labour MP who has spent his political career calling for radical overhaul of the UK economy.

While in reality his ideas may not constitute a wholesale overthrow of capitalism, they are nonetheless more controversial than any which have thus far been proposed by a major political party.

They include dramatically raising taxes on the wealthiest earners, bringing them back to 1970s levels; stripping the Bank of England of its independence; forcibly splitting up Britain's banks; abolishing all business tax breaks and introducing price controls on energy, rail and bus fares.

And all these on top of the controversial policies put forward by Mr Corbyn, including the nationalisation of Britain’s rail, energy and banking systems, and "people’s quantitative easing", under which the Bank of England would print money to finance public investment projects.

Of course, we have yet to learn whether all or indeed any of these policies will find their way into Labour’s next manifesto, but they nonetheless raise a question: do they suggest that Britain and its electorate are moving leftwards, or are they a cry of desperation from a Labour party frustrated with years of suppression?

It will take some years to find out the answers. In the meantime, we now have more ideological distance between the two major parties in Parliament than ever before.

Another question is whether that will drag the Conservatives to the centre, as they attempt to win over moderate Labour supporters, or push them further to the right, in the absence of strong centrist opposition.