Reform UK’s election successes show the party can cause as grave a headache for Sir Keir Starmer as for Kemi Badenoch. One of the first things Mr Farage said when he finally won a parliamentary seat in July was: “We’re coming for Labour – be in no doubt about that.”

The victory in the Runcorn and Helsby by-election demonstrates that voters in Labour-held territory will back Reform if they are angry with Sir Keir’s party. This will fuel fears that Labour strongholds, such as the Welsh Valleys, which did not turn blue in Boris Johnson’s 2019 landslide could swing behind the Farage phenomenon.

There is strong concern that while many voters in former industrial heartlands could not bring themselves to vote Tory, there is no such stigma about voting Reform. Sir Keir’s leadership is under attack from Left-wingers who say his policies have alienated traditional supporters.

Labour MP Richard Burgon said: “Labour’s defeat in Runcorn was entirely avoidable – and is the direct result of the party leadership’s political choices. By pushing policies like cuts to disability benefits and scrapping the winter fuel allowance, the leadership is driving away our own voters – and letting Reform squeeze through.

“The Labour leadership must urgently change course and govern with real Labour values to deliver the change people are crying out for.”

It seems counter-intuitive to say Labour is vulnerable to Reform attacks because it is not Left-wing enough. But new polling shows Reform supporters are to the Left of the general public on key issues.

Find Out Now polling for Apella Advisors found that 67% of Reform voters think “services such as water, rail and energy should be run by the public sector” – this compares with 57% of the wider public. Likewise, 69% said “foreign ownership is a bad thing”, which is the view of less than half (47%) of the general public.

James Kirkup, of Apella Advisors, said: “Nigel Farage’s recent embrace of Left-wing economic language appears to be resonating with his voters and could win over significant numbers of Labour voters. By following this trend in public opinion, there’s a chance that Reform could shape political debate around economics in the way that they have influenced the conversation about migration.”

That’s quite a thought – that the rise of Reform could push the UK, economically at least, to the Left.

But the possibility presents Morgan McSweeney and other key Labour thinkers with a challenge they need to start addressing long before the next Westminster election. How do they tackle a party that can simultaneously compete with the Conservatives on the Right and Labour on the Left?

Cool heads will point out that the Runcorn by-election was held in exceptional circumstances, after the incumbent Labour MP admitted repeatedly punching one of his constituents in the street. Reform won by a mere six votes – this is not conclusive proof of a historic realignment in British politics.

But it would be foolish in the extreme to assume Reform will fizzle out. Populism is now a major force in the UK.