“MY DAD will turn in his grave,” admits Gerard Richardson, a Whitehaven wine merchant, “but I’ll vote Conservative.” How many others feel this way? On February 23rd Labour will find out when it defends two by-elections in England. Neither Copeland, on the north-west coast, nor Stoke-on-Trent Central, in the West Midlands, has ever been represented by another party. Yet bookmakers reckon at least one of the strongholds, and perhaps both, will change hands because voters like Mr Richardson are so fed up.

Labour has been sliding in the polls since choosing Jeremy Corbyn, a hard-leftist, as its leader in September 2015 (see chart). Brexit has made things worse: though the party backed Remain, the majority of the constituencies it represents voted to Leave. Mr Corbyn now has net-unfavourable ratings among men and women of all age groups, in all social classes, in all regions, and of all party affiliations—including Labour.

The two campaigns show how Labour faces threats in its heartlands from different sources. In Stoke, the challenge comes from the insurgent, populist UK Independence Party. Paul Nuttall, UKIP’s new leader, is putting his credibility on the line by contesting it, vesting his hopes in a campaign focused on Brexit and immigration. “We have to take one to two thousand votes off Labour, especially on the council estates,” explains Mick Harold, chairman of the local branch. Grand civic buildings like the town hall (which could double as the palace of a minor European royal family) recall Stoke’s history as a centre for pottery and steel production. But the days when there was a “pot bank [pottery factory] on every street”, as locals like to say, are long gone. So are the steelworks. The old warehouses are now used by retail and industrial firms to store and distribute stock. Work there is low-paid and low-skilled, attracting immigrants to the town but leaving it poor. Whole rows of shops are boarded up. Stoke Central was in the most pro-Brexit tenth of Britain, with 69% for Leave.

Copeland also voted for Brexit, but there the threat to Labour comes from the Conservatives, who are hoping to become the first party in government to gain a seat from the official opposition in a by-election since 1982. In Whitehaven, the biggest town, Georgian terraces and a redeveloped harbour belie local hardship. Yet there is money in the area. The nuclear decommissioning plant at Sellafield provides 10,000 well-paid jobs, lifting wages a quarter above the national average.

Amid struggling towns and former pit communities, there are farms and chintzy tourist villages. It is one of the largest and least populous constituencies in England (“There’s always another mountain to drive around,” complains a Tory MP from a nearby seat). The 2011 census found that 98% of residents were white. “Immigration is not an issue in this area,” admits Fiona Mills, UKIP’s candidate, whose leaflets give more prominence to the National Health Service (NHS) and nuclear industry.

Mr Corbyn’s scepticism about nuclear energy has been poorly received, but Labour’s Copeland branch is “so pro-nuclear we glow in the dark,” one councillor says. The news that Toshiba may pull out of a deal to build a nuclear power station at nearby Moorside may harm the Tories a bit (on a visit to Copeland on February 15th Theresa May would not say whether her government would rescue the project). And Labour is better positioned on the NHS, the other big issue. Maternity services at a local hospital face cuts.

Can Labour hang on? The bookmakers have the Tories down as favourites in Copeland. In Stoke, Mr Nuttall once looked like a shoo-in. But, not for the first time, UKIP’s organisational incompetence may prove its downfall. Labour is precision-targeting its voters with messages about how Mr Nuttall used to want to privatise the NHS. His credibility has been damaged by his admission that an earlier claim that he had lost “close personal friends” in the Hillsborough football disaster of 1989 was false. Bookies that made UKIP the favourite at first now think Labour will prevail.

Defeat in either constituency would put Mr Corbyn under new pressure. Already he is vulnerable: his weak performance in recent debates on Article 50, the mechanism for launching EU exit talks, was the final straw even for some of his left-wing allies. But he is unlikely to quit in the coming months. He may not want to fight the next election, in 2020, as leader but he does want to quit the job having secured the left’s control of the party.

That means building up a preferred successor—possibly Rebecca Long-Bailey, the new shadow business secretary—and changing the party’s rules to lower the number of nominations by MPs needed for a leadership candidate to go before members. Having defeated his party’s moderate wing in two successive leadership contests, the latest only last summer, for now Mr Corbyn is in control of his departure date.