Humza Yousaf is developing a standard off-hand response to defections.

After going 89 years without one in a parliament, the SNP has now had two in a month. 

You might think that’s a bit of a red flag, that serious thought is required.

But so far the First Minister has been glib and petty.

When Dr Lisa Cameron crossed over to the Tories at Westminster, Mr Yousaf shrugged: “It’s the least-surprising news I’ve had as leader of the SNP, I must confess.”

She “probably never believed in the cause in the first place”, he suggested.

And when former minister Ash Regan joined Alba just sixteen days later, Mr Yousaf sneered that it was “no great loss to the SNP group” and “not a surprise either”.

In both cases, he urged the person to do the honourable thing and resign their seat despite dreading another by-election after defeat in Rutherglen.

It was a superficial, kneejerk response intended to show indifference in the hope that voters won’t pay too much attention.

But given the unprecedented nature of these events - at least for the SNP - that is wholly inadequate. 

It may be true that both Dr Cameron and Ms Regan were half out of the SNP when they quit.

The former was about to be deselected, while the latter was likely to face it soon enough.

But it still takes a lot for a politician to switch parties. Something must be badly broken.

Both women had been ostracised for failing to toe the party line.

Dr Cameron complained of a “toxic” culture in the SNP Westminster group.

A friend of Ms Regan told the Herald that she had been “treated like s***” by her fellow SNP MSPs after daring to stand against Mr Yousaf in the leadership contest.

The treatment illustrates the dark side of the SNP’s grip on power.

Add in disagreements over how to achieve independence, multiple policy splits and growing alarm about Labour's revival at the general election, and you have a very volatile mix.

Party sources said Ms Regan’s defection could set off a “domino effect”, with other elected politicians and activists crossing to Alba. 

The prospect of experienced foot soldiers switching sides ought to be particularly worrying for Mr Yousaf, given the SNP’s problem mobilising its own people in Rutherglen.

It cannot afford to lose more activists going into an already grim election.

What happens next?

The political grapevine is alive with rumours that Alex Salmond also has an SNP MP waiting in the wings for the second day of his conference on Sunday.

That was his modus operandi when he announced his party's creation in March 2021.

First, he wheeled out former SNP justice secretary Kenny MacAskill as Alba’s first MP.

The following day he produced newbie Neale Hanvey as its second.

No one in the SNP would be surprised if the old showman did it again.

As for Mr Yousaf’s hope that voters won’t notice? Of course they will.

Divided parties always attract attention - and their problems usually snowball.