Labour leadership vote: Principles versus power

There are small nations that don't have an electorate as large as this. Today, Labour begins sending out 640,000 ballot papers to members and supporters who must now decide the future of Britain's main opposition party.

The scale of this election is incredible - one in every hundred people in Britain has a vote. And by now, their choice is pretty clear.

With barely a ballot paper between the policy positions of Owen Smith and Jeremy Corbyn, this race is really about principles versus power.

Owen Smith is essentially the 'power man'. A good communicator with the backing of his parliamentary colleagues, he repeatedly claims that he's the more credible Prime Minister-in-waiting. And the argument goes that without power, you can't achieve Labour's principles.

For Jeremy Corbyn, on the other hand, it's principles first, power second. Much of his appeal is grounded in his integrity - a man who's spent a lifetime defying pressure in pursuit of his beliefs. Though his reluctance to compromise is partly why critics claim he's unelectable as Prime Minister.

Whether Labour supporters prioritise principles or power will decide this contest, but probably won't settle it. It is virtually impossible to imagine hundreds of Labour MPs falling into line behind a victorious Jeremy Corbyn, or thousands of enthused Corbyn supporters suddenly switching their allegiance to Owen Smith.

Whether or not there are splits or coups, Labour is about to enter the final phase of what is an existential crisis. How does a modern opposition party combine principles with power? What compromises does it make and what purpose does it serve? Beneath the surface of the leadership contest, this is the real struggle taking place.