Scottish politics has “fundamentally changed” as a result of Labour’s emphatic win in the Rutherglen & Hamilton West by-election, Anas Sarwar has said.

The Scottish Labour leader said the result was the culmination of years of voter discontent with the SNP and Tories and a desire for change.

Labour outpolled the SNP two-to-one in the marginal seat south east of Glasgow, winning 17,485 votes to the SNP’s 8,399 on a swing of 20.4% and a turnout of 37.2%.

The Tory vote collapsed from 15 to 3.9%, costing the party its deposit, as Unionist appeared to vote tactically to deny the SNP a win.

It was the first Westminster seat the SNP had ever lost in a by-election, having previously only lost the Holyrood seat of Dunfermline to Labour in 2013.

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Humza Yousaf admitted the result was “disappointing”, while SNP Westminster leader Stephen Flynn said the party must not shy away from the scale of the challenge it faces.

The by-election was triggered by voters ousting former SNP MP Margaret Ferrier in a recall petition over her breaking Covid rules. 

Ms Ferrier had a majority of 5,230 over Labour in the 2019 general election. Labour’s Michael Shanks yesterday won by a majority of 9,466 over the SNP’s Katy Loudon.

Speaking on BBC Radio Scotland, Mr Sarwar said: “I think it was genuinely a historic night in Scottish politics. I think Scottish politics has fundamentally changed. 

“I think it's no exaggeration to say we didn't expect it to be as good a result as it was. 

“And I think it demonstrates that people across Rutherglen & Hamilton West are tired of two failing governments, they’re tired of the incompetence, the division, the chaos, and are crying out for a fresh start, they’re crying out for change, and the vehicle for that change is Scottish Labour.”

Pressed on his claim that Scottish politics had fundamentally changed given it was only one by-election with a specific backdrop, Mr Sarwar doubled down on the remark.

He said: “The reason why I think it is a fundamental change is this wasn't a result that was two months or six months in the making, it was years in the making. 

“When I became leader two years ago, we were 32 points behind the SNP in the opinion polls, people were talking about Scottish Labour’s survival.

“For us two years on to win a parliamentary by-election for the first time in more than 12 years in Scotland, to get more than double the vote share of the SNP, and to get a swing of more than 20% is seismic, it is huge, it’s significant.

“But don't get me wrong, we’ve still got work to do. And one promise I can make to people right across Scotland is I'm not complacent about that. 

“I wasn't complacent when I became a leader two years ago. 

“The same energy, the same humility, the same commitment that I've demonstrated the last two years I will do between now and the next general election and beyond. 

“Because I am desperate to deliver change for this great country.”

Pushed on whether voters actually liked Sir Keir Starmer and Labour, Mr Sarwar said: “We would not have had the result we had last night if it wasn’t for the hard work and the change that Keir Starmer has delivered right across the UK.

“Because people in Scotland can see that you have a UK Labour Party that can actually beat this Conservative party. 

“We had our worst election results since the 1930s just three years ago. And Keir Starmer in that three years has got in a position where we can actually beat the Conservatives across the UK. 

“I think the public has decided that they want the Tories to lose.  I think they can see this as an end-of-days government. 

“I think people in Scotland have decided and can see that the SNP has now lost its way.  It's incompetent, arrogant in power, and has got 16 years of failure. 

“They're looking for an alternative, and my task is to build the alternative. 

“This is one staging post. We still have work to do between now and the next general election, and indeed between now and the next Scottish Parliament election, because I don't want to just win that election because the SNP and the Tories deserve to lose, I want to win it because Labour deserve to win. 

“And that means building on the policy platform we've already set out. For example, clean energy by 2030 with GB energy, a publicly owned energy generation company headquartered in Scotland. Our new deal for working people. I could list many, many more. 

“I want us to build upon that platform programme as we head towards that next general election.”

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Reminded more people voted for Labour in Rutherglen & Hamilton West in 2019 when the party lost the seat than on Thursday (18,545 to 17,845), Mr Sarwar said the lower turnout in the by-election (37.2% to 66.5% in the general election) was “not unusual”.

He said: “I honestly believe, going into a general election, we will have an even stronger message because ultimately in by-elections, what people can do is send a message to failing governments, they can tell you what reaction do you want, but they don't actually have the opportunity to change a government. 

“The difference going into the next general election, people in Scotland and right across the UK will have the opportunity to actually get rid of this economically illiterate, morally bankrupt Tory government and they know that the vehicle for change for that is Scottish Labour MPs and voting Scottish Labour.”

Reminded Labour would not be able to flood every seat with the same level of money and manpower seen in Rutherglen at the election, Mr Sarwar admitted resources and effort would not be concentrated in the same way, but spread over a broader front.

However he added: “I think it's also important to recognise that the scale of the campaign, both in terms of what's happening in the airwaves but also on the doorsteps is going to be even bigger than what it was in Rutherglen & Hamilton West. 

“And I'm really really confident as we head towards that general election that will continue to build our capacity, we will continue to build up our volunteer base, we will continue to make the argument and win the argument that if you want change in this country, there is now only one unrivalled party of change and that is Scottish Labour.”