Britain's opposition Labour Party leader Ed Milliband listens to speakers during the party's annual conference in Manchester on Sept. 22. Reuters

MANCHESTER, England—The U.K.'s opposition Labour Party pledged Tuesday to give the state-run National Health Service a £2.5 billion ($4.1 billion) annual boost if it wins the coming general election, funded by a levy on high-value homes, new fees on tobacco companies, and a clampdown on tax avoidance by companies.

In his keynote speech at the center-left party's last autumn conference before the May election, Labour leader Ed Miliband sought to position his party as the protector of the health service.

The service, created by Labour in the 1940s, is considered a national treasure by many in the U.K. and one of the country's biggest employers. Labour has accused the coalition government of needless reform and seeking to privatize its services, which are free.

To pay for the additional funding, Mr. Miliband said he would raise £1.1 billion by clamping down on tax avoidance by hedge funds and other companies, and introducing fees for tobacco firms based on those introduced by U.S. President Barack Obama, which would raise at least £150 million. The fees for individual tobacco firms would be based on their market share, Labour said.

The party didn't give a figure for how much it expected to raise from the levy on homes worth more than £2 million, dubbed the "mansion tax." That measure has been championed by the Liberal Democrats, the smaller party in the governing coalition, but opposed by Prime Minister David Cameron's Conservative Party.

A key challenge for Mr. Miliband heading into the election is convincing voters and the business community that he can manage the U.K. economy, which is growing at a solid rate again following a deep recession when Labour was last in power.

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However, in a fresh sign that the party's plans are irking businesses, the Tobacco Manufacturers' Association, which represents the views of the industry, said the measures were illogical.

"Rather than coming up with ways to attack a legitimate U.K. business sector, the Labour Party should be thinking of how to claw back the billions in revenue the government loses through sales of illegal tobacco in the U.K.," said Giles Roca, the association's director general.

Imperial Tobacco Group PLC said the idea of targeting a sole business sector with an additional tax was unjust and should be dismissed immediately.

Mr. Cameron has sought to force Mr. Miliband on two key issues. One issue involves how much say other parts of the U.K. have on strictly English matters. This issue came to the fore in the wake of last week's Scottish referendum when Mr. Cameron, in an effort to appease some English members of his own party, promised greater autonomy for England as well as for Scotland.

The other issue is on EU membership, with Mr. Cameron having promised a referendum on the U.K.'s membership by the end of 2017 if he is elected in May. Mr. Miliband Tuesday reaffirmed his commitment to EU membership.

The Labour leader reiterated his pledge to help working families. A key message he has pressed to voters is that the government's austerity drive has led to a severe drop in living standards after several years in which consumer prices have risen faster than wages, fueling what it has dubbed the "cost of living crisis."

Labour has previously announced plans to introduce measures—such as retail-energy price freezes and an increase in the minimum wage—intended to show they are fairer than the Conservative Party. The Conservatives have accused Labour of being antibusiness and some of the measures have been criticized by business groups.

"There's no doubt that Ed Miliband has ambition for Britain and we share his desire to build more homes, raise living standards and remain in a reformed European Union," John Cridland, the director-general of the Confederation of British Business, the U.K.'s biggest business group, said in a statement. "But we heard very little about how to create the economic growth to deliver these ambitions and the crucial role of healthy and thriving businesses in creating prosperity for all."

Labour Party members who came to hear Mr. Miliband's speech, which lasted just over one hour and was delivered without prompts—a feat that has become his calling card in such occasions—said the National Health Service was an issue that everyone cared about and reiterated the view that the Tories couldn't be trusted to look after it.

"The NHS is the crown jewel for the U.K. and Miliband is spot on that it needs saving," said Emma Toal, 25, councilor in Harlow.

Mr. Cameron has repeatedly pledged that the health service would be safe in the Conservatives' hands and the coalition government has shielded it from swinging budget cuts it has levied since coming to power in 2010. But Mr. Miliband said the health service faced huge challenges in the coming years.

"We will set aside resources so that we can have [in] our NHS, 3,000 more midwives, 5,000 more care workers, 8,000 more GPs, and 20,000 more nurses," the Labour leader said, prompting applause and a standing ovation from the party faithful.

Labour holds a narrow lead in polls over the Conservatives. A survey of 1,671 adults by pollsters YouGov PLC shows Labour with 35% of support among voters and the Conservatives on 33%. However, the polls show Mr. Miliband rates less well than Mr. Cameron, with YouGov reporting that just 15% of people think that the Labour leader has provided an effective opposition to the government and 68% saying he hasn't. Eighteen percent say he would be up to the job of prime minister, while 63% say that he wouldn't be.

As well as developing the health service, Mr. Miliband said in his speech that Labour would target five other goals: raising the national minimum wage, promoting new home construction, increasing apprenticeships, helping self-employed people, and fostering green industries.

Gary Ransford, 54, a Labour supporter who works with disabled people, said Mr. Miliband had laid a few good foundations for the election campaign but there was unlikely to be a landslide victory in 2015.

"He's [Mr. Miliband] better than Cameron and Clegg put-to-bloody-gether," he said, referring to Deputy Prime Minister Nick Clegg. "There's no doubt about his capabilities, but there is a long way to go yet and there's no time for complacency."

—Peter Evans contributed to this article.

Write to Nicholas Winning at nick.winning@wsj.com