(Bloomberg) -- Keir Starmer accused former Brexit campaigner Nigel Farage of making promises to British voters that the country cannot afford, in a preview of what polls suggest could become a key political battle over the next five years.

“If you don’t fund your manifesto, you just say you can have anything you like or anything you think is important,” Starmer told LBC radio, when asked why his poll-leading Labour Party won’t match a pledge by Farage’s insurgent Reform UK party to boost welfare support for some families. “Every single thing we are putting in our manifesto is fully costed and fully funded, and we’re going to say before the election the things we can’t afford to do.”

The question is sensitive because many in Starmer’s party, including ex-premier Gordon Brown, agree with Farage that the UK’s two-child limit on welfare payments for parents should be scrapped should the party emerge victorious in the country’s general election on July 4. Erasing child poverty is regarded as a political issue Labour typically tries to claim as its own. 

But while Starmer expressed sympathy for the proposal, he reiterated Tuesday that an incoming Labour government would face stretched public finances. 

“One of the problems in politics is that before an election people say I’m going to do A, B and C and then after the election they don’t do it,” he said. “We don’t have a magic wand; there isn’t enough money available” to scrap the cap. He nevertheless added that his party in government “will have a policy for reducing and eliminating child poverty.”

The remarks underscore how Farage has upended the UK election campaign since making a sudden decision to stand as a Reform UK candidate in the seaside town of Clacton, pledging a “political revolt.” On Monday he published his party’s electoral manifesto — which he called a “contract with the people” and described as “unashamedly radical” — while conceding it wasn’t designed to be deliverable.

“This is not something with which we’re going to govern the country,” Farage said. Economists including the influential Institute for Fiscal Studies said Farage’s sums didn’t add up.

Farage’s candidacy has galvanized Reform, which on Tuesday rose to a record 14.4% in Bloomberg’s poll of polls, a rolling 14-day average using surveys from 11 pollsters. 

One YouGov poll last week showed Reform ahead of Rishi Sunak’s governing Conservatives for the first time, and the immediate threat to the Tories is a further split in the right-wing vote which the prime minister has repeatedly warned would allow Labour an easier path to victory. In Britain’s first-past-the-post voting system, even a significant lift in Reform UK’s popularity is not expected to yield more than a handful of seats in the House of Commons.

Yet Farage’s re-appearance in front-line British politics poses a risk to Labour too. In the short term, Britons who voted Conservative in 2019 but were leaning toward Starmer’s party — especially in battleground seats in Labour’s former heartlands in northern and central England — could yet be swayed by Farage.

Since taking over from socialist leader Jeremy Corbyn in 2020, Starmer has battled against Tory accusations that a Labour government would raise taxes and be profligate with the public finances. That explains why Starmer and Rachel Reeves, who would be Britain’s first female Chancellor of the Exchequer if Labour wins as expected, are constantly challenged to rule out various tax rises and repeatedly commit to sticking to tough fiscal rules on borrowing.

But Farage is playing a different game. In announcing £90 billion ($114 billion) of tax cuts and £50 billion of spending increases in some areas including the National Health Service, Reform UK is not promising a plan for government but a policy platform to beat Labour with for five years in government. 

Farage also wants to make next month’s vote  an “immigration election” by tying Britain’s economic and social problems to high net migration, a reprise of the 2016 Brexit campaign he is mostly known for.

There have been familiar setbacks — though Farage has also tried to dismiss them with his trademark chutzpah. He blamed a “vetting” firm contracted by Reform UK for failing to discover candidates with links to a British fascist leader and who had previously expressed admiration for Adolf Hitler’s tactics.

“We have been stitched up politically,” Farage told LBC on Tuesday.

Reform UK’s growing popularity on the right of British politics raises key questions for Sunak’s Tories, especially in the event of a landslide Labour victory. Some Conservatives including former Home Secretary Suella Braverman want to see Farage and potentially other Reform MPs welcomed into the Tory party.

Others will balk at onboarding some of the extreme views expressed by some senior Reform figures, including calling on the UK to repel asylum-seekers in the English channel using military force. But the governing party is clearly rattled by Farage’s entry into the race, and has deployed former Prime Minister Boris Johnson — still popular with the party base despite being forced out of the top job by his own MPs — to rally support.

“It’s great that Boris is supporting the Conservative Party,” Sunak told reporters on Tuesday. “He’s endorsing many candidates in videos and letters which we’ve coordinated by the campaign and every week he’s making that case in his column, and I know that will make a difference.”

For Starmer, the risk is entirely different. The Labour leader has promised the return of political integrity after what he calls 14 years of Conservative chaos, or a “politics which treads lighter on people’s lives.” 

Farage, for his part, appears hell-bent in the longer-term on shifting the political ground in a way that more traditional politicians like Starmer often struggle to counter. His stated aim is to secure a “bridgehead” in the Commons at next month’s vote, that he can use as a launchpad to a wider assault on the UK’s traditional Tory-Labour duopoly in the next election, due by 2029.

--With assistance from Alex Wickham.

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