Five years after deciding to phase out the use of coal, Britain took steps on Wednesday to address some of the country’s largest remaining sources of greenhouse gas emissions, announcing plans to end the sale of new gas and diesel cars within a decade and change the way people heat their homes.

The plans are expected to be a centerpiece of Prime Minister Boris Johnson’s effort to put pressure on other countries to reduce their emissions in the run-up to major climate negotiations Britain will host next year. And they were an early signal to President-elect Joseph R. Biden Jr. that Britain and the United States might find common cause despite the looming tumult of Brexit, which Mr. Biden opposed.

Climate activists cast the announcement as Britain’s most ambitious step to protect the planet since it decided to end the use of coal, but questions remained about parts of the plan.

It relies on technologies — like the use of hydrogen to heat homes — that some analysts caution have been oversold. The overall levels of investment fall far short of the tens of billions of dollars in climate-related spending recently pledged by Germany and France. And some analysts said the plan did not do enough to encourage businesses to invest in clean energy jobs in Britain.

“Successive British governments have done an excellent job of ensuring our country has quickly switched from coal and gas to clean sources of electricity,” said Joss Garman, the U.K. director of the European Climate Foundation. “But this announcement from the prime minister is really the first time we have witnessed a similar level of ambition to curb pollution from cars and home heating.”

It remains to be seen, he said, whether the government is prepared to spend enough to realize its ambitious goal of net zero carbon emissions by 2050.

For a country where electric vehicles account for less than seven percent of new car purchases, Mr. Johnson’s decision to ban the sale of new gas and diesel vehicles by 2030 amounted to a strong signal to consumers and manufacturers alike. (In a minor concession to Toyota, which manufactures some hybrid cars in central England, Britain will allow the sale of some hybrids until 2035.)

To support the move to electric vehicles, Mr. Johnson said the government would spend 1.3 billion pounds, or $1.7 billion, installing charging points, and hundreds of millions of pounds in grants for consumers to make the cars more affordable.

Even so, analysts said the government was not doing enough to support the production of electric vehicle batteries, presenting major challenges to a motor vehicle manufacturing industry that employed 166,000 people in Britain as of 2018. Britain’s departure from the European Union has already caused investment in the auto industry to plummet.

“Without additional government help, without additional companies coming in, the U.K. automotive industry is going to struggle to survive the transition to electric vehicles,” said Peter Wells, the director of the Centre for Automotive Industry Research at Cardiff Business School.

By 2030, improvements in electric cars and the related infrastructure may make persuading people to buy them much simpler. But analysts said it was still significant that the government was going beyond setting new product or industry standards and actually impinging on consumers’ choices.

The 2030 ban includes gas and diesel delivery vans, a likely mainstay in the post-pandemic economy. That was “a very clear sign” of the government’s determination, said John Gummer, Lord Deben, the chairman of the Climate Change Committee, a watchdog that monitors progress on emissions reductions. “They wouldn’t have put it in if they were just window dressing.”

Since Britain won its bid to host international negotiations over climate change in Glasgow next year — an event that some analysts see as the most significant the country has hosted since the 2012 Summer Olympics — the government has faced pressure to set the bar high for arriving world leaders.

Those pressures only grew with the election of Mr. Biden, who is eager to elevate climate change issues in his administration but much less enamored of Britain’s departure from the European Union.

Some members of Mr. Johnson’s Conservative Party, particularly those aligned with his recently departed chief adviser, Dominic Cummings, have argued that a focus on clean energy would make people peel away from the party in struggling industrial areas that switched to supporting the prime minister in last year’s election.

But Mr. Johnson, who has a history of sometimes casting doubt on climate science, is now trying to cast his plans as a boon for jobs and businesses in those regions, like the Midlands.

Offshore wind farms, which Mr. Johnson put at the top of his green list, are helping to create jobs in areas that were once heavily industrialized, as are plans involving the oil giants BP and Equinor to capture carbon dioxide emitted by local industries in these regions and pump it into a reservoir beneath the North Sea.

“Imagine Britain when a Green Industrial Revolution has helped to level up the country,” Mr. Johnson wrote in the Financial Times on Tuesday night, suggesting that the plans could create 250,000 green jobs. “You cook breakfast using hydrogen power before getting in your electric car, having charged it overnight from batteries made in the Midlands.”

For the most part, the sort of culture war over climate science that has helped stymie action in the United States has failed to take root in Britain.

A recent survey by Climate Outreach, a non-profit group, together with YouGov, a respected polling firm, showed that only 3 percent of respondents in Britain did not think climate change was real. Nearly 60 percent of people said they wanted the political party they voted for to do more to slow climate change.

“Policymaking must catch up with the public desire for action,” Mr. Garman said.

Beyond its problems with road traffic emissions, which analysts say stem from busier roads and sales of sport utility vehicles, Britain has also struggled to reduce emissions from heating its notoriously leaky homes.

To address that, Mr. Johnson’s new plan set a target of 2028 for annually installing hundreds of thousands of heat pumps, a more efficient system than the typical gas boiler. The government also extended a program of vouchers for people making energy efficiency improvements to their homes, and announced investments in trials for the use of hydrogen in heating and cooking.

Like Japan and Germany, Britain has increasingly looked to hydrogen as a way of lowering emissions. The cleanest form of hydrogen — so-called green hydrogen, which is usually generated from water using clean electricity sources like offshore wind — is still expensive to make. But advocates say that with economies of scale and technical advances those costs will come down.

Britain’s nuclear industry, which accounted for 17 percent of electricity generation in 2019, was also encouraged by the government’s mention of supporting both large- and small-scale reactors.

But with the coronavirus pandemic having battered Britain’s economy, the prime minister’s plans only included 12 billion pounds, or $16 billion, in new spending, large chunks of which had already been pledged.

Nick Mabey, chief executive of E3G, an environmental group, said he doubted the government was doing enough to attract the private investment needed to make a success of its green plans. “This doesn’t quite get over the bar,” he said.