The referendum debate enters a new phase today with the launch of the latest adverts by both campaigns.

For the Yes side, there is a poster featuring the word 'can't' altered to spell 'can' while on the No side, there is an advert featuring ordinary Scots who support the Union. Scotland can have more powers for the parliament and more job opportunities as part of the UK, says the Better Together poster; it can have the best of both worlds.

The tone of the adverts should come as no surprise. For a long time, there has been a perception among voters that the No side has been overly negative and the perception is now influencing both campaigns, with the Yes poster specifically seeking to exploit the feeling, and the No advert attempting to redress it.

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The impression of an overly negative message is clearly also worrying some in the No campaign - as it should. Speaking to The Herald today, a senior Coalition source said ministers were being overwhelmingly positive but that change was needed. "Most of what we say is very positive," he says, "but it is the negative parts that are attracting attention."

To what extent this supposed negativity is affecting the polls is hard to tell, although the latest poll for ICM suggests support for No has fallen from 46% to 42% in a month while support for Yes has remained steady.

The First Minister Alex Salmond's take on these figures is that support for the Yes campaign is growing because it has been positive and his opponents have been negative; the Better Together campaign director Blair McDougall on the other hand says that while a positive case is important, he also has a duty to highlight what he sees as the risks for Scotland in going it alone.

In reality both sides have been negative about their opponents' arguments, with the Yes campaign criticising the UK and the No campaign criticising the idea of independence. But for the No camp, there remains a danger in voters becoming tired of a negative tone discussing the risks of independence - and voters rebelling against it.

What the No campaign must do now is set out a more positive agenda and learn what it can from the Yes side. Both sides must also recognise their responsibility to disseminate as much information as possible while also guarding against the dangers of complacency.

There are some on the No side who have taken their lead in the polls for granted; the risk for Yes is that they assume the momentum will remain with them.

Hopefully, the adverts appearing in newspapers from today signal a new direction. Some of the big players will also be intervening in the debate this week with the Labour leader Ed Miliband visiting Glasgow and the former prime minister Gordon Brown delivering his first speech under the Better Together banner.

They have a responsibility to point out the risks of independence as they see them, but it appears that the No campaign has finally accepted that it is much more likely to win with a positive campaign and a list of strong, compelling reasons to stay in the UK.