Much at stake for SNP in the Granite City

Most observers believe the SNP will win comfortably on June 20. The by-election follows the death, after a courageous battle with cancer, of SNP MSP Brian Adam, who had represented the area since 1999 and was widely respected not just locally but by political friends and foes alike at Holyrood.

Wisely, the Nationalists have chosen a well-kent candidate in Mr McDonald, who stepped down as a North East list MSP to fight the seat and whose CV includes a spell working for Mr Adam. They also have healthy majority to defend. At the last election in 2011 Mr Adam defeated Labour's Barney Crockett – now the leader of Aberdeen Council – by 7175 votes, taking a 55% share to his main rival's 28%.

On paper it should be an SNP procession. Why then, is it starting to look like a proper scrap? Some clues were in the campaign messages coming out of the Granite City yesterday. Strategists on all sides know defeat for the SNP, however unlikely, would wipe out Mr Salmond's majority at Holyrood, and their pitch to voters is based partly on that intriguing possibility. So we heard Labour candidate Willie Young telling folk: "The only thing Alex Salmond is interested in protecting is the majority he needs to keep the Scottish Parliament talking endlessly about separation and ignoring the priorities of ordinary Scots." Meanwhile we heard Mr Salmond claiming that popular SNP policies such as the council tax freeze and free prescriptions would be at risk if he lost his majority because "they require to be supported each and every year through the Scottish Parliament's budget process".

Both parties are guilty of overstating the case. We should really not get too excited about the potential loss of the SNP's majority.

Defeat in Donside would leave the party with 64 out of Holyrood's 129 seats but, on most issues, Mr Salmond would retain the support of many from the non-SNP 64 (if you are wondering why that adds up to 128, the Presiding Officer is neutral). They would include Jean Urquhart and John Finnie, who left the SNP over its decision to support Nato, and Bill Walker, who was thrown out over allegations about his private life. With the independence-supporting Greens and Margo Macdonald also in the non-SNP 64, it's hard to imagine that life for the Government would, in practice, become any more difficult. Losing his majority might give his opponents a symbolic boost but it would not give Mr Salmond sleepless nights. It would be business as usual at Holyrood.

What the Aberdeen Donside result will give us is an indication of whether the bitterly fought independence campaign is affecting the SNP's broader popularity.

The First Minister has endured a difficult time as rows over an independent Scotland's currency, membership of the EU and armed forces have dominated headlines but will all that make voters think twice about voting SNP? Labour believes it will and party bosses are keen to put the theory to the test.

All political parties are notoriously cautious as they try to manage expectations before a by-election. Looking ahead to June 20, the SNP would tell you any victory for a party in mid-term Government was impressive going while Labour would insist eating into the Nats' majority in a safe seat was good progress for them.

But behind the spin the SNP want to win well and there are some at least in Labour who believe they could cause an upset if they threw the kitchen sink at their campaign, not least because the party has a track record in the area in Westminster and council elections.

There is plenty at stake, then, if not quite the collapse of Holyrood as we know it. The Aberdeen Donside by-election will only rise up the national political agenda as we move towards polling day.