BEING an ordinary sort of parent, news junkie and Netflix dependant, I never seemed to find the time to read a great many books over the summer, certainly not as many as I wanted.

But among those I did read was Dictator, the third part of Robert Harris’s trilogy about the great Roman orator and senator Cicero. There’s a passage in it that keeps nagging me.

Referring to the triumvirate – the coalition of Julius Caesar, Pompey and Crassus that ran the Western world before turning murderous – the narrator says: “Whenever a thing seems at its zenith, you may be sure its destruction has already started. So it was with the triumvirate.

“It towered above the landscape of politics like some granite monolith. Yet it had weaknesses that none could see and which were only to be revealed with time.”

Harris, of course, is more than an historical novelist. A former political reporter, he was, until Iraq, a friend of Tony Blair and had a ringside seat when New Labour was at its peak. So that observation is very probably a statement on the Blair-Brown duumvirate too.

It’s equally applicable to Scottish Labour, which has gone from granite monolith to loose chippings of late.

In retrospect, we can see the erosion began years ago, which brings us to the SNP, which towers over Scotland in Labour’s stead.

With thousands gathering for its largest ever conference this week and Nicola Sturgeon dominating headlines, it might seem an odd moment to ask if its decline is also underway. But away from the multiple ovations in the main hall, the cracks are starting to show.

At a fringe meeting yesterday, Alex Salmond’s former chief of staff, Geoff Aberdein, advised Nicola Sturgeon to hold a second referendum promptly.

Lots of SNP members want a swift referendum because they thirst for independence.

But Mr Aberdein’s logic had a sting in it. Given political gravity affects all parties, he said this might be Ms Sturgeon’s last chance before the SNP’s popularity dips and there is a Unionist majority at Holyrood after 2021.

Ms Sturgeon says she has a mandate for a referendum. It could be use-it-or-lose-it time.

The improbability of a deal with Westminster on Brexit is another push factor. Not only did the First Minister raise the bar on Thursday by throwing in extra demands, there’s also the obvious question of why the UK Government should bust a gut to create a deal for an insatiable SNP.

Even if Westminster gift-wrapped it, any deal would only be a stop-gap for the SNP.

I asked one of Ms Sturgeon’s inner circle what would happen if the UK met the party’s every Brexit demand and asked in return for independence to be taken off the table. “Ah,” he smiled, “we are the SNP after all.” In other words, it’s never off the table.

But, and it is a very big but, Ms Sturgeon might not want a referendum. She could lose. Her career would probably be over and her cause would be in tatters.

It might be logical, and it might leave her alive to fight another day, but what would her party think?

She said not a day passed without someone advising her both to hurry up and slow down with a referendum. But whatever she did, she told her audience: “I know I can count on your support every step of the way.”

But could the SNP stay united if Ms Sturgeon disappointed a vast chunk of the membership by backing off a referendum? “They trust her,” nodded one of those close to her.

Easy to say but if, as Mr Aberdein fears, the SNP goes backwards in 2021, a large number of the party would surely be furious that the First Minister had failed to take her chance.

Brexit is creating another kind of strain. One-third of SNP voters supported it. And, as one young delegate told me, he and other Leavers aren’t happy about the party leadership demonising Brexit and trying to make it synonymous with the Tories and xenophobia.

Until Brexit, he’d never disagreed with Ms Sturgeon but now he disagreed more and more.

“There’s more of us than you think. Nicola says she wants to bring the Europeans back. I want controlled immigration. I’m hearing things [from the leadership] I want to escape from.”

There is a sense of accumulating tension. People realise the party is entering a critical phase. Of course, SNP granite may be tougher than I think. No doubt the good people on Twitter will put me right.

Still, I can’t get that passage from Robert Harris out of my head.