The man once regularly cited as Scotland's most senior civil servant, Sir John Elvidge, established himself as someone worth listening to both in and out of office.

Unusually for those immersed in it, he also has a sense of the world outside politics.

So when he ventures an opinion on the referendum on Scottish independence, it is worth paying attention to.

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Mr Elvidge is concerned that the referendum debate has become polarised and divisive, so much so that by the time of next year's vote it could leave a legacy of long-term damage to society. People could be so divided by the way they choose to vote in the referendum that a toxic after-effect could blight Scotland for years to come, he told an all-party Parliamentary Group on the Constitution at the House of Lords.

His seven years as permanent secretary to the Scottish Government merit respect. But how realistic is his claim? It echoes that of Andrew Marr, when he warned recently that the independence debate could unleash a toxic brand of anti-English feeling.

So how toxic is the public discourse about independence? It is worth remembering that members of smaller would-be states around the world seeking more self-determination looked on in wonder as the UK and Scottish Governments agreed to a democratic debate and a straight vote on Scotland's future.

In many countries, the idea of independence without violence let alone rancour seems fanciful. But in Britain and in Scotland the discussion is more reasoned.

Yes, there is polarisation and, whichever option wins next September, there will be aggrieved losers and disappointed campaigners. Also, Mr Elvidge is right to suggest that a close vote, and continued pressure for further referendums, could be unsatisfactory for both sides. Still it seems unlikely, given the secret ballot, that Scots will be defined or divided by who was on which side on referendum day, as he argues might be the case.

There is an issue about the legacy of the debate itself. In particular, there is a need for both sides to consider how Scotland can move forward after the poll. Whatever the outcome, Scotland needs to emerge a confident nation, with a positive vision of itself, whether within or outside the UK.

Mr Elvidge also claims the international community would aid a newly independent Scotland and ensuring it received a fair financial deal. Meanwhile he sees few barriers to maximum devolution as an alternative if independence is rejected.

His suggestion that Orkney and or Shetland might choose to secede from Scotland is unhelpful and unrealistic, not least because polls suggest few Orcadian or Shetland residents would support the idea. This has overtones of the kind of scaremongering many voters are already finding tiresome.

However, Mr Elvidge's comments have emerged when the Yes Scotland camp in particular faces increasing calls to be more aggressive and less polite. In that context his observations are timely.