IT seems so straightforward.

According to the White Paper on independence, in the event of a Yes vote, Scottish universities would continue to charge annual fees to students from the rest of the UK (rUK) of up to £9000, while at the same time offering free tuition to those from Scotland.

No protracted legal wrangles, no threat to Scottish students, no impact on the income to Scottish universities from fees. Business as usual in the international powerhouse of Scottish higher education.

In fact, conventional thinking thus far has suggested the opposite would be the case.

The current charges to rUK students are possible because, under European Union (EU) law, separate countries within one state, such as the UK, can operate different fee policies, whereas countries that are independent of one another, such as France and Germany, cannot. So, because universities in England charge their students fees of up to £9000 a year, Scottish universities can too, while retaining free tuition for Scots.

However, in an independent Scotland that remains part of the EU, students from England, Wales and Northern Ireland would become EU students and have to be given parity with those from Scotland and have their fees paid. That would mean the end of a vital stream of income for universities, likely to be worth at least £140 million by 2015-16.

So where does the confident assertion in the White Paper come from that all will continue as it currently does? Interestingly, the only legal advice on the issue that has reached the public domain, commissioned by lobbying group Universities Scotland, does appear to offer that possibility.

The advice rests on just two cases, both of which were unsuccessful because the European Court ruled the countries involved had failed to prove there was sufficient reason for them to discriminate against students from elsewhere in the EU.

However, there is a potential loophole for the SNP. The court suggested it might be possible to justify a difference in treatment to students from another country if they risked the very existence of a national education system. So the Scottish Government might be able to discriminate by charging fees to rUK students, but only if it successfully argued higher education was "imperilled" by the prescence of rUK students.

That is exactly what the White Paper points to. It recognises the "substantial numbers" of students from elsewhere in the UK already coming to Scottish universities and acknowledges the different fee policies post-independence would create a "huge financial incentive for students from England to study in Scotland".

If the Scottish Government argued successfully such an influx jeopardised places for Scots and robbed the economy of the graduate skills it needed then, potentially, its fees policy could be retained.

However, relying on the "unprecedented position of a post-independent Scotland" rather than established case law, with no prior judgement as to what constitutes a threat to a national education system is a far more uncertain position than the White Paper suggests.