Do not be negative:

the message seems to be getting through. David Cameron's visit to Scotland yesterday will have raised anxiety levels at Better Together HQ, the Eton-educated English Tory Prime Minister not being the best recruiting sergeant for the cause.

Yet when Mr Cameron opened his mouth, it was at least to put the positive case for the UK, after weeks of growing complaints about the negativity of the No campaign. The Prime Minister was careful to note that "of course" Scotland would have a share of defence and security resources if it were independent (no scaremongering there) but he wanted to stress the advantages it had as being part of the UK, in international diplomacy, being a leading member of Nato, the EU, the G7 and G20, as well as shared military, security and counter intelligence services.

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He also cast himself as a pro-devolution Prime Minister, stressing that a No vote would ensure more powers for Holyrood, addressing the charge that he could not be trusted to keep his promise.

As Prime Minister he has every right to come to Scotland, of course, and at least from Better Together's perspective there were no own goals, but do his visits help the No campaign?

It is a safe bet that those most offended by having an English Conservative Prime Minister will already be in the Yes camp. At the same time, some undecided voters will be prepared to listen to what the Mr Cameron has to say. Even so, being head of a party with only one MP in Scotland diminishes the Prime Minister's moral authority. In January 2012, Mr Cameron challenged Alex Salmond to accept an offer from Westminster to hold an early, legally binding referendum. The Prime Minister was perhaps emboldened by polls at the time giving the pro-UK cause a 25-point lead.

The political landscape has changed. The pro-Union campaign remains firmly in the lead but that lead has shrunk. The overarching problem it has is that charge of negativity. A TNS poll this week noted that 53% of people consider the Better Together campaign has been negative while only 29% believe the Yes campaign has been.

At around the same time, the First Minister made a highly personal attack on Mr Cameron, describing him as personifying everything that was wrong with UK politics. In spite of that negative tone and the fact that the SNP's campaign has focused heavily on talking down the Westminster Government, the charge of negativity is far less harmful to the pro-independence campaign than to opponents. Better Together insist with some justification that their positive messages are frequently overlooked by journalists but the fact remains that there was a spell in winter when the UK Government let loose one attack on independence after another. The charge of negativity then was entirely justified.

The pro-UK cause may benefit from more positive campaigning but, with the Prime Minister being a turn-off to many, it continues to lack a figurehead to match Mr Salmond.