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What do Tony Blair and Jeremy Corbyn have in common?

Very little, one might think, but since being elected leader of the Labour Party in 2015, Mr Corbyn has apparently come to share the view Mr Blair expressed in his memoirs that "a political party needs to be led strongly and a strong leader needs loyal supporters".

"If you think the leadership is wrong or fundamentally misguided, then change leaders; but don't have a leader and not support their leadership," he wrote.

"That way lies political debilitation."

In the event that the Parliamentary Labour Party (PLP) disagrees substantially with the person the members have chosen, their collective wisdom should not prevail over the judgement of the leader.

Their only option should be to go for broke and try to elect another leader.

That has not, historically, been the way the Labour Party has worked.

Before Mr Blair, decision-making was less concentrated in a small group, subject to groupthink.

It was more of a collective endeavour in which the shadow cabinet (the cabinet when the party was in government), the party's National Executive Committee (NEC) and the PLP all had their parts to play.

A leader had to retain the confidence of all of these bodies.

All three, however, have been weakened over the past two decades.

Mr Blair and his closest allies downgraded the policymaking role of the NEC and attempted to amass power in the leader's office.

As the Chilcot Report is but the latest to observe, Mr Blair too often bypassed the cabinet and, in the crucial issue of Iraq, failed to have a properly constituted Cabinet Committee, one that should have included among its members the Leader of the House and former Foreign Secretary Robin Cook, who would have added the penetrating scrutiny and informed judgement that was sadly lacking.

There was a partial return to more cabinet government under Gordon Brown, but Mr Brown, too, was a hoarder of power who liked to determine policy within a group of like-minded people.

Image copyright Wales News Service Image caption Tony Blair's 1998 cabinet: Many believe Mr Blair sought to consolidate power in his personal office

However, an initiative that has inadvertently helped to land Labour in its current crisis was, ironically enough, that of Ed Miliband, the most collegial of the last three Labour leaders before Mr Corbyn.

Mr Miliband won support for a fateful decision (applauded by Mr Blair) to stop members of the Parliamentary Labour Party from electing the shadow cabinet, placing instead this power of appointment in the hands of the party leader.

Leaders and their aides tend to short-sightedly favour enhancing the leader's power while they are the beneficiaries, without thought to the same powers passing to a radically different leader and regardless of the folly of concentrating power in the hands of any one individual and his acolytes.

Had this potential weakening of a collective leadership that could command the support of the parliamentary party not been endorsed by the PLP itself and, subsequently, by the Labour Party as a whole, the present standoff between Mr Corbyn and the great majority of the PLP could have been ended with less damage to what is, after all, the country's main alternative party of government.

A shadow cabinet representative of opinion within the PLP would have remained in place and collectively taken decisions.

If a party leader differed fundamentally from the majority of such a shadow cabinet, the onus would be on him or her either to persuade colleagues that they were mistaken or to come to an accommodation with them.

If unable to do the former and unwilling to do the latter, the only alternative would be resignation.

Image caption Under Ed Miliband, the power to select Labour's shadow cabinet went to the party leader

The notion that the vote of party members (including newly enlisted associate members) for a particular leader should turn MPs into party delegates, there to do the bidding of the leader (assumed to be the very embodiment of the party), is at odds with the principle of parliamentary democracy, and the idea of the leader as boss is not part of the ethos of social democratic parties.

Moreover, it was not only the party leader, but every Labour MP who was selected, in the first instance, by party members and, subsequently, endorsed by the broader electorate.

The majority of the PLP who have already publicly expressed their lack of confidence in the current leader, triggering the leadership contest in which Mr Corbyn's post will be contested, may belatedly realise that they should never have given up their power to choose the members of the shadow cabinet.

When the party leader and the majority of the parliamentary party are utterly at odds, effective opposition to the government in the House of Commons is unsustainable.

At the same time, it has been far from unreasonable for Mr Corbyn and his supporters to point to the substantial majority he gained in the leadership election only a year ago and to the increased membership and activity of the party in the country.

Image copyright Getty Images Image caption Jeremy Corbyn is supported by the grassroots group Momentum

There is force in the argument that the value of party membership is drastically reduced if a leader who has widespread support in the constituency parties (although, given the consequences of his election, not necessarily majority support) is prevented from contesting a new election for fear he might win.

The National Executive Committee has now ruled that Mr Corbyn is automatically entitled to a place on the ballot, even if he cannot muster the support of 51 MPs or MEPs.

Although it is unprecedented for a leader to be determined to remain in office with such modest parliamentary support, there is no doubt that the legitimacy of a new leader will be far greater if she or he has won an intra-party election in which Mr Corbyn was a candidate.

That things have reached this point is strange indeed.

In whichever manner Labour leaders have been elected - and it has been by different rules and different constituencies at various times - they have usually spent a lengthy time in that position.

The party has been far from ruthless in removing them.

It has generally been electoral failure, leading to voluntary resignation by the leader, or premature death, as in the cases of Hugh Gaitskell and John Smith, that has produced change at the top.

It is, however, unparalleled for more than three-quarters of the Parliamentary Labour Party to have publicly declared their lack of confidence in their leader - and surprising for the leader to wish to continue in office in those circumstances.

That made another leadership election unavoidable.

Archie Brown is emeritus professor of politics at Oxford University and author of The Myth of the Strong Leader: Political Leadership in the Modern Age.