Britain’s governing Conservative Party on Friday lost two of its safest parliamentary seats in a significant and ominous setback for the prime minister, Rishi Sunak, who must call a general election that will decide his fate within the next 15 months.
Voting in the Conservative strongholds of Mid Bedfordshire and Tamworth took place on Thursday to replace two of the party’s lawmakers — one of whom quit after an allegation of sexual assault — and came as Britain’s health care system faces acute strain and its economy stagnates amid high inflation.
While that was always likely to put the Conservatives under pressure, the double defeat in the party’s heartlands was a stunning blow to Mr. Sunak and a striking success for the opposition Labour Party and its leader, Keir Starmer.
In Tamworth, northeast of Birmingham, Labour overturned a majority of almost 20,000 in the last general election to win narrowly, while in Mid Bedfordshire, around 50 miles north of London, the main opposition party overcame an even bigger deficit to seize the seat.
Mr. Starmer described the vote as “a phenomenal result that shows Labour is back in the service of working people and redrawing the political map.”
In a statement, he added: “To those who have given us their trust, and those considering doing so, Labour will spend every day acting in your interests and focused on your priorities. Labour will give Britain its future back.”
Analysts caution against over-interpreting these types of local contests — known as by-elections — where there is no prospect of the result changing the government, and voters often cast their ballots to register a protest against the governing party. Less than 36 percent of registered voters turned out to vote in Tamworth; in Mid Bedfordshire the number was higher, at 44 per cent.
Because the Conservatives won so convincingly in the last general election, in 2019, Labour has an electoral mountain to climb if it is to win a clear majority the next time Britons are asked to decide who should govern them.
Yet, the scale of the switch of votes revealed on Friday does not bode well for Mr. Sunak, suggesting that even some of his Conservative Party’s more secure strongholds are no longer impregnable. It will also increase Mr. Starmer’s confidence that, having shifted his party to the political center ground, he can win an outright majority in the next general election.
“This isn’t destiny, but it is a pointer that unless the Conservatives can fairly dramatically and fairly radically turn things around, then they are, in truth, staring defeat in the face in 12 months’ time,” John Curtice, a professor at the University of Strathclyde and a leading polling expert, told the BBC early Friday.
The first result to be declared was from Tamworth, where voters were choosing a successor to Chris Pincher, the former Conservative lawmaker who had represented the district. He resigned from Parliament after a drunken incident in which, it was alleged, he had groped two men.
In the last general election in 2019, Mr. Pincher won with a majority of 19,634, but on Friday that was overturned when the Labour candidate, Sarah Edwards, won 11,719 votes, and the Conservative candidate, Andrew Cooper, 10,403.
“Tonight the people of Tamworth have voted for Labour’s positive vision and a fresh start,” Ms. Edwards told her cheering supporters after the result. “They have sent a clear message to Rishi Sunak and the Conservatives that they have had enough of this failed government.”
Support for Brexit was strong in Tamworth, and Labour’s victory will encourage it to think it is winning back voters who had deserted it for the Conservatives because they favored Britain’s exit from the European Union.
In Mid Bedfordshire the contest was to replace Nadine Dorries, a former cabinet minister and prominent supporter of Boris Johnson, who quit as prime minister last year. Ms. Dorries announced her intention to leave Parliament in June when Mr. Johnson stood down as a lawmaker, but she caused confusion by delaying her formal resignation and faced accusations of absenteeism and failing to represent local voters.
In the 2019 general election, Ms. Dorries won a majority of 24,664 over Labour, and the Conservatives had represented the district since 1931.
That ended on Friday when Labour’s candidate, Alistair Strathern, won 13,872 votes, the Conservatives came second with 12,680, and the smaller, centrist Liberal Democrats won 9,420.
Both results were a stinging blow to Mr. Sunak, who, since he became prime minister last year following the brief and disastrous leadership of Liz Truss, has failed to close a persistent double-digit deficit in the opinion polls against the opposition Labour Party.
Mr. Sunak was praised for restoring some measure of stability after Ms. Truss’s economic plans roiled the financial markets and she became the country’s shortest lived prime minister in history. But he has struggled to win over the British public after 13 years of Conservative government.
In recent weeks, Mr. Sunak has tried to seize the political initiative with a series of eye-catching decisions: scaling back climate change targets, canceling the second phase of a high-speed rail project, announcing new measures to phase out the sale of cigarettes to young people and proposing a shake-up to the high school examination system.
Little electoral reward appears to have flowed from these announcements, however, three of which were made at the Conservative Party’s annual conference in Manchester earlier this month.
That meeting was distracted by a high-profile appearance by Ms. Truss, and by scarcely concealed jockeying from those who see themselves as contenders for the party leadership, should the Conservatives lose the general election.
By contrast, Labour’s conference in Liverpool, the week after, presented a more unified and confident image of a party that sees itself as close to power.
Friday’s results are the latest in a succession of election setbacks for Mr. Sunak. In July Labour won a by-election in Selby and Ainsty, in the north of England, overturning a Conservative majority of more than 20,000.
Earlier this month, Labour unseated the Scottish National Party from the Rutherglen and Hamilton West district, in a result that underscored a revival of the main opposition party’s fortunes in Scotland. Success there during the next general election could significantly improve Labour’s prospects of forming the next government.
Conservative officials played down the significance of the results on Friday, pointing to the low number of voters who turned out, and to the circumstances surrounding the resignation of the lawmakers who had represented the two districts.
But Mr. Curtice, the polling expert, that “no government has hitherto lost to the principle opposition party — in a by-election — a seat as safe as Tamworth.” He also recalled that the Conservatives had lost a similar election in the same region, then named South Staffordshire, in 1996.
The following year, Labour won a landslide general election victory under Tony Blair.