“Shy” Reform voters in Labour areas led to Nigel Farage’s party winning the Runcorn by-election by just six votes, Labour peer Harriet Harman said.

The Runcorn and Helsby seat, created in 2024, went to Reform UK’s Sarah Pochin who defeated Labour candidate Karen Shore by six votes.

Reform overturned a 34.8% majority gained by former Labour MP Mike Amesbury last year before he stood down earlier this year after he punched a constituent on a night out.

It is the closest by-election result since records began in 1945.

Read more: Badenoch apologises to Tory councillors

Labour peer and former minister Baroness Harman told Beth Rigby on the Electoral Dysfunction podcast: “If we’d have known it was so close, I, myself, would have gone on extra time there and got those six votes.

“So, there’s a real level of frustration and I’m sure there’ll be a post-mortem, but I think there’s a lot of talk about shy Reform voters in Labour areas.”

In the local elections, running at the same time, the Conservatives lost control of all 18 councils it was contesting, with Reform taking eight of those.

The party also won two of the six mayoral contests – Reform’s first two mayors.

Baroness Harman said Labour now has “got to get on with delivering on the health service” and pointed out the minimum wage increase and breakfast clubs are only just being rolled out.

But she said the government also needs “more of a story” instead of just telling people to “bear with us” while it fixes what the Conservatives did.

“It seems to be that Farage has got no delivery, as yet, and all the story, whereas the government is really getting on with delivery, but it hasn’t got a big enough story about what that fits,” she said.

Read more: Reform’s political earthquake is now shaking our political system

She added that “Blue Labour” MPs – a socially Conservative wing of the Labour Party – “will be emboldened to press for further action” on issues like immigration, which they want to see a tougher stance on.

“There’s been grumbling about the big salience of the concerns of the winter fuel payment, but I don’t see there being any change on that,” she said.

Baroness Harman said she does not think the by-election and local election results were “utterly predictable” and will not lead to any splits or instability within the party.