In Series One of the West Wing, Mallory, a public sector school teacher, breaks off a nascent relationship with White House staffer Sam Seaborn for writing a position paper in support of school vouchers. Mallory says, "I thought we had something going on and yet you haven't told me you favour school vouchers? ... I despise you and everything you stand for."

School vouchers, and other policies which channel public funds into private education, are not just of interest to policy wonks - they provoke visceral, even violent reactions from the public. Chile's school voucher programme ignited mass protests in the Penguin Revolution of 2006, and the Chilean Education Conflict of 2011-12, which involved hundreds of thousands of students over a period of more than half a year.

In the US, school vouchers are one of the most contentious issues in politics, whilst - as Michael Gove's performance at the Leveson Inquiry demonstrated - the mere suggestion of allowing private companies to run state schools for profit in the UK invites flurries of denunciation in the strongest possible terms.

Few issues engender such public squeamishness. So much so that a development which seems like the natural conclusion of Coalition education policy was definitively taken off the table by Nick Clegg, who in 2011 declared, "Yes to greater diversity; yes to more choice for parents. But no to running schools for profit, not in our state-funded education sector."

And yet in Sweden, legislation allowing profit-making companies to run schools was passed in the early nineties without political fanfare or public discontent. In fact, it has been suggested that the Swedes are possibly less interested in their own free school system than we are. So why might this be?

The idea of the state paying for some children to attend private schools - whether that is achieved through school vouchers, or funding for-profit free schools - is more problematic, and more contentious, in countries with high levels of inequality. In the US, in Chile, and in the UK, it reignites the perennial debate about selective versus comprehensive systems - do we use public funds to empower a finite number of lower-income children to succeed, or do we try to raise the level of the entire system? In countries like Sweden, where inequality is low, and free schools are well integrated into an education system with one of the most radical comprehensive traditions in the world, it is much less of an issue.

A recent OECD paper investigated the impact of voucher-style policies on socio-economic inequality. It found that, whilst 'universal' voucher systems which offer vouchers to all pupils significantly increase levels of inequality, countries with 'targeted' voucher systems which only make vouchers available to lower-income students have similar levels of inequality to countries which don't use such systems at all.

Alan Milburn, the Government's independent adviser on social mobility and a longstanding advocate of school vouchers, renewed his call for a 'targeted' voucher scheme in an interview with the Times last week, outlining a model which would enable parents with children at failing state schools to send them to a state or independent school of their choosing. The Sutton Trust has also called for a targeted scheme which would provide state subsidies for bright children from lower-income families to attend private schools at a rate of £5,500 per pupil. Meanwhile, Policy Exchange has proposed a model of 'social enterprise school' which would allow 50 per cent of any school surplus to be paid out in dividends according to a 'John Lewis'-style system of mutual ownership.

In whatever guise, this is an issue that is unlikely to go away. Michael Gove's comments at the Leveson Inquiry have been the most forthright statement to date of the Conservatives' position on schools being run for profit. And yet in marked contrast to his Coalition partner, Gove has been circumspect in his public statements on the issue - even now ruling out the change before the possibility of majority Conservative rule returns post-2015. As he fully realises, this kind of policy has the power to wreck more than one politically-charged relationship.

The Associate Parliamentary Group for Skills and Employment is holding a seminar on the profit motive in education on 12 June in parliament. A pre-seminar report, 'Profit in education: where we are now', can be downloaded here.

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