potentially paying more than was necessary and the tax being impossible to collect on graduates who emigrated. Adam Smith Institute proposal In 2017, Dr Madsen Pirie of the free-market think tank Adam Smith Institute proposed a graduate tax in the Institute's A Millennial Manifesto publication: it suggested a tax of 5% levied on graduates earning over £22,500 in income, rising to 8% for those earning over £30,000. It also suggested that there should be no interest charged, instead indexing the amount each year in line with inflation. Justine Greening Former Education Secretary and Conservative MP Justine Greening proposed a graduate tax in 2018. Greening outlined a plan for a 'higher education fund' in which all graduates earning above £25,000 would pay into through a 9% levy on income over a 30-year period. Furthermore, Greening suggested that employers could also contribute to the fund to support degrees that had benefited their organisations. “Pure” graduate tax A distinction is sometimes made between a "pure" graduate tax and other forms of graduate tax or similar funding proposals. A "pure" graduate tax often entails a levy imposed on graduates throughout all or most of their productive lives, set at fixed rates by the government, continuing even well past the point a graduate has repaid the original costs of their higher education, and could also be retroactively applied. This is in contrast to more flexible forms of graduate tax where, for example, the tax would be lifted once the graduate had repaid the costs of their education plus interest. Economist Nicholas Barr argued that a "pure" graduate tax system would suffer from what he called the "Mick Jagger" problem: some higher earners who had attended university would in theory end up effectively financing a large part of the system, creating incentives to emigrate and risking the stability of the system. Similarly, former Business Secretary Sir Vince Cable referred to problems over emigration when he ultimately rejected a "pure" graduate tax in 2010 during the Browne Review into higher education. Comparisons to the current fees system Numerous comparisons have been made of the existing tuition fees system in the UK and its similarities to a graduate tax. In 2010, the Institute for Fiscal Studies (IFS) in analysing Lord Browne's proposals (much of which would later go on to be incorporated as the existing tuition fees system), explained that the system being proposed was structurally similar to