LONDON, June 17 (Xinhua) -- Britain's Prime Minister Theresa May has announced Sunday that the National Health Service, which celebrates its 70th anniversary this year, is to be given a financial boost worth nearly 27 billion U.S. dollars a year.

May said much of the extra funding would come from the money saved by Britain not having to pay its multi-billion dollar levy once it leaves the European Union.

May, trailed her plans ahead of a major key note speech Monday when she will announce more details of how the extra spending will be funded.

During the campaign leading up to Britain's EU membership referendum in 2016, a bus toured the country saying departure from the bloc would save Britain 350 million pounds a week (465 U.S. dollars) with a message saying much could be used for the NHS.

The promise on the bus caused controversy, with Remain campaigners saying it hoodwinked many people to vote to leave the EU.

In media interviews May said the NHS birthday present would exceed the 350 million pounds a-week extra promised by Leave campaigners during the EU referendum campaign. Her five-year plan covers just front-line health budgets overseen by NHS England.

Political commentators say the extra cash could also be partially funded by a specific NHS income tax on top of general taxation.

Health Secretary Jeremy Hunt said then spending program would be achieved by giving the NHS a fitting birthday present for what he described as Britain's most loved institution.

Hunt said: "It recognises the superhuman efforts made by staff over the last few years to maintain services in the face of rapidly growing demand. But it also presents a big opportunity for the NHS to write an entirely new chapter in its history."

The government has faced heavy criticism this year for under funding of health services, with complaints of long waiting times for patients and sick people waiting on trolleys in hospital corridors to be seen by doctors.

Niall Dickson, CEO of the NHS Confederation, which represents healthcare organisations, said the announcement, which represents a 3.4 percent rise in the NHS budget, isn't a bonanza by any means and falls short of the 4 percent extra-a-year figure suggested by an independent report.

Dickson added: "It's a lot better than we've been used to over the last few years."

The main opposition Labour Party described May's funding offer as a hypothetical windfall for the NHS.

Labour's shadow health secretary Jonathan Ashworth said: "Today's announcement confirms that Theresa May has failed to give the NHS the funding it needs.

He said the government was asking patients to rely on a hypothetical Brexit dividend.

May's spending boost for the NHS dominated the front pages of some of Britain's national Sunday newspapers.

The Mail on Sunday headline read "May's 20 bln pounds NHS gamble" with a sub-heading adding the prime minister is betting the public will be willing to face tax hikes for better care.