The agreement signed by Scotland's First Minister Alex Salmond and the UK Prime Minister David Cameron today will ensure that the future of Scotland is determined in a referendum in the autumn of 2014.

As with any deal following prolonged political negotiation, both sides claim success in achieving their aims. In this case, Mr Salmond has obtained the timing he wanted and an extension of the franchise to 16 and 17-year-olds. Mr Cameron has succeeded in restricting the options on the ballot paper to a single question for or against independence.

The political spin over whether the Scottish Government ever really wanted a second question will continue. But now that agreement has been secured to lower the voting age, the practical matter of how to ensure all those who have reached their 16th birthday by the date of the referendum are able to vote becomes critical.

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Under the Section 30 Order transferring control of the referendum from Westminster, Holyrood will gain the power to extend the franchise but there are practical difficulties in ensuring that everyone who qualifies by age will be added to the electoral roll. At present only those who will become 18 on or before November 30 the following year can be included as "attainers".

Those who are currently in that category can be assured they will be able to vote. In some parts of Scotland, attainers have already cast their first ballot in health board and crofting elections.

However, a mechanism must now be found to enable those who are currently 14, 15 and 16 to be registered, possibly, since this is currently a reserved matter, by creating a separate register for the referendum. If teenagers are required to apply individually, there is a danger that many will be left out; the process must include all who will qualify.

The practical difficulties are such that some at Westminster claim conceding to this demand from the SNP has presented Mr Salmond with a poisoned chalice. As The Herald reports today, however, the Scottish Government is confident that it has found a solution to the difficulties that will overcome the technical and legal problems.

This is essential. If 16 and 17-year-olds are to be given the vote, there must be effective measures to enable them to exercise it or the Scottish Government will fall foul of human rights legislation. In addition to the well-rehearsed arguments for lowering the voting age (that 16-year-olds can marry and be required to pay taxes but have no say in how they are spent), the reason put forward for specifically giving them a vote on independence is that they have more invested in the future of the country than any other age group.

A measure intended to extend democracy to them must not become a travesty of the principle. The consequences of this referendum are so great that every aspect must be a model of fairness.