Perhaps it was just me but at last week's annual spring conference of the SNP on the banks of the Clyde it seemed that some of the euphoria of recent Nationalist events was beginning to evaporate.

If you had been at any of last year's gatherings, you would have found it difficult not to be swept along by their fervour. Last week's event in comparison was like attending a Coldplay concert the week after you've been to see AC/DC: everyone was in a jolly good mood but there was no blood, sweat and tears.

Perhaps this is what happens after more than two years of endless jelly and ice cream in which 100,000 are added to your numbers. During this time you have been at the centre of the most seismic period of UK political history since the 1832 Reform Bill; in fact you have been the cause of all the tremors and eruptions. You can't keep waving flags and shouting at the top of your voice all the time and, anyway, the shops are running out of selfie-sticks.

"What happens," a respected, Nationalist-leaning commentator mused last year "when all these new members and their new delegates find their feet within the party and begin to ask some tough questions?" What I think he was getting at was this: the SNP had marginalised the Labour Party in Scotland by portraying itself as the natural party of the left and anti-austerity.

In doing so, they had taken advantage of ordinary Labour supporters' anger at their leaders' enthusiasm for sharing platforms with the Tories during the independence referendum campaign. At some point though, when the streamers and party hats have been put away and people are getting bored of making fun out of dim Labour councillors on social media, they turn round and begin to inspect the furniture in their new home.

Over the last few years Labour grandees such as Gordon Brown, Alistair Darling and John Reid failed abjectly to judge the mood of their own supporters in their Scottish heartlands. This was hardly surprising as each of them looked and sounded like they would need a sat-nav to find these places. The SNP though, must not make the same mistake of misjudging the mood of their new adherents and assuming their loyalty in perpetuity.

There was a reason why Scotland's most disadvantaged communities voted for independence and it wasn't all because of a deeply-help love for Auld Scotia and your wee bit hill and glen. In Labour's traditional redoubts in Glasgow, Dundee, North Lanarkshire and West Dunbartonshire many people were beginning to feel the economic chill of the Conservative government and chafe at how they weren't all in it together.

The traditional Tory Party battle-cry of "Some are More Equal Than Others" has never been more loudly proclaimed than by the current incarnation, notwithstanding Iain Duncan Smith's late conversion to the cause of Mother Teresa. Labour supporters in these places didn't like the direction in which society was moving again under the Tories but they liked even less London Labour's facile response.

Yet, whereas prior to 2014 they felt they had no alternative but to continue voting for the same, smug old faces in Scottish Labour for Westminster and perhaps tweak their tails at Holyrood, now there was an alternative: the SNP in an independent Scotland. This party sounded like it meant business and they made a convincing case over the course of a two-year independence campaign for the notion that not only was Scotland a fairer country than England but that Labour was part of the pattern of inequality south of the border.

So; where are the policies that will deliver Scotland's working people from wicked Westminster's fell economic grip? According to an election leaflet I received at my home the other day only the SNP will protect the NHS; invest in education; build affordable homes; compensate for Tory austerity and reform land ownership legislation.

The party, though, has been in power for nine years in Scotland and nothing remotely like any of this has happened. They seem reluctant to encourage innovation in the one-size-fits-all approach to delivering state education and the goal of relieving pressure on hospital A&E wards by increasing primary care remains a distant dream.

On land reform two things have happened which ought to alarm the SNP. The first is that the people of Scotland are waking up to this issue and how it encapsulates unfairness and inequality in this country more than any other. Second is that they have allowed the Greens to drive land reform through Andy Wightman, the brilliant campaigner and writer.

Wightman could have been a powerful voice inside the SNP but has always been treated with contempt by some senior party figures who always conspired to ensure that he was kept away from addressing conference fringe meetings on land reform.

At their conference last week I asked a Nationalist MSP about the strange reluctance of the SNP to scare the horses and take some risks. After all, by the time Labour become a threat once more the party are likely to have been in continuous power for almost 20 years. No other government in the western world has been given a mandate such as this.

If Nicola Sturgeon wanted to introduce rations and national service in the next parliament she'd still get elected next time around. "What's the point in risking any big moves prior to this election," my Nationalist friend told me. "Just watch our agenda in the next parliament. This will be the first one Nicola has begun as leader, so she'll put her stamp on it from the outset."

She had better soon. During an impressive keynote speech to the Scottish Labour conference one week later Kezia Dugdale, who is palpably growing into the job of Scottish leader, asked this: "If the SNP haven't delivered the change you want to see with the experience of ten years in power, with a lead in the opinion polls, with a majority in Parliament, will they ever deliver?"

It won't vex the SNP overmuch that their main opponent is asking this but it ought to trouble them that some who voted Yes are beginning to ask the same question. How the party chooses to answer it in the next parliament will have a significant bearing on its ability to deliver a Yes vote at the next independence referendum.

Commentary from Kevin McKenna, writer and broadcaster. Kevin is a former deputy editor of the Herald and executive editor of the Scottish Daily Mail. His journalism regularly appears in the Observer and the National.