Katy Loudon was a far better candidate than the SNP deserved.

She knows the patch, she’s competent, and she's a grafter.

She’s well-liked by locals, and inspired loyalty from activists. 

The party was lucky to have her. 

READ MORE: Rutherglen and Hamilton West: Labour score historic victory

Being a by-election candidate in any circumstances is difficult.  Being the candidate when your predecessor was found guilty of wilfully exposing her constituents “to the risk of infection, illness and death” is on another level.

Throw in the police investigation into the SNP’s funding and finances, the arrest of Nicola Sturgeon, and party splits and internal criticism over their record in government, and the task becomes almost impossible.

And yet she was out, nearly every day, smiling, taking the abuse, making the case, talking to voters. 

The SNP's defeat in Rutherglen and Hamilton West cannot be blamed on the candidate.

This is the party's defeat, this is Margaret Ferrier’s defeat, but mostly this is Humza Yousaf’s defeat.

We know this because during the campaign, he was clear, the buck stops with him.

With the party faithful gathering in Aberdeen next week at their conference, his already wonky leadership is now badly damaged. 

Why should party members listen to him when he sets out his independence strategy? 

Why should they back his plan for most seats equals Indy talks?

READ MORE: Rutherglen & Hamilton West by-election LIVE: huge Labour win

Meanwhile, Labour’s ambition of winning 20 plus seats at the next election now looks easily achievable. 

Professor Sir John Curtice even suggested they could pick up 42 if the by-election result is replicated across the country.

That's one more than they lost in 2015.

It means Sir Keir Starmer’s chance of winning a majority in the Commons looks all but assured. 

The first red wall to fall has another brick. That's still only two bricks, but it's momentum.

He’ll be here early on Friday morning to personally congratulate his new MP, and he goes into this weekend's party conference with a huge spring in his step.

Labour always thought they were going to win, but nobody, absolutely nobody thought they'd win with a margin like this. 

Never mind Sir Keir moving into No 10, after a result like this, Anas Sarwar can probably start thinking about measuring the curtains for Bute House.