Hospitals will bear the brunt of “incredibly shortsighted” cuts to public health initiatives that will lead to more people having a heart attack or getting cancer, experts are warning.

New research reveals that, by next year, spending per head in England on programmes to tackle smoking, poor diet and alcohol abuse will have fallen by 23.5% over five years.

Key services, including those to help people quit smoking, manage their sexual health or stay off drugs, are among those being subjected to the deepest cuts, according to analysis by the Health Foundation thinktank.

Public health funding will continue to be slashed despite the extra £20bn that Theresa May has pledged to give the NHS by 2023-24. The public health grant that the Department of Health and Social Care (DHSC) gives to local councils in England, which is not covered by the cash injection, is due to fall from £2.44bn this year to £2.27bn in 2019-20. It will be the fifth year in a row it has been cut since its peak of £2.86bn in 2014-15.

By next year, councils will be spending £95m on smoking and tobacco-control services, 45% less than they were in 2014-15. The next biggest cuts over that period will have occurred in drug and alcohol services for under-18s, down by 41% to £40m, and the equivalent services for adults, which will have fallen by 26% over those five years. Sexual health services will also be getting 25% less.

“There’s a massive gap between the government’s rhetoric on public health and prevention and the reality,” said Tim Elwell-Sutton of the Health Foundation. “NHS England’s Five Year Forward View talked about ‘a radical upgrade in prevention’ while in her recent speech about the NHS the prime minister said ministers would support public health. But we are seeing significant cuts to public health budgets. It is incredibly shortsighted not to invest in keeping people well. We are storing up problems for our health and also for the NHS, which is already under huge pressure. It could become increasingly unsustainable as more and more people with preventable illnesses will need long-term healthcare.

“We’re crazy if we’re not taking seriously the underlying cause of one of the most harmful illnesses – cancer – which is also one of the most expensive to treat,” said Elwell-Sutton. Although smoking rates are falling, the habit leads to almost 500,000 hospitalisations a year and is a major cause of strokes, heart problems and life-threatening respiratory conditions.

Shirley Cramer, chief executive of the Royal Society for Public Health, accused ministers of “confused thinking” over health. “These figures demonstrate a frustrating contradiction from the government, whereby welcome extra money is given to the NHS with one hand, while the other generates more strain on NHS services by draining public health and prevention.”

Conservative-controlled Warwickshire county council is the local authority where the public health grant has been cut the most – by 39%, or £40 a head – since 2014-15. Other councils which have seen their budgets shrink by substantial amounts include Knowsley in Merseyside (38%) and Wokingham in Berkshire (38%). Five councils have seen their budget rise, including Shropshire (up 17.4%) and Warrington (up 11%).

Cramer voiced concern that two of the councils which have seen their public health grant cut the most, Knowsley and Tameside in Manchester, are also among the 10 areas with the highest rate of people being admitted to hospital because of poisoning by drugs, and three others are in the top 40.

The Department of Health and Social Care said: “We have a strong track record on public health – smoking levels are at an all-time low, rates of drug misuse are lower than 10 years ago, and drug addiction treatment services remain free for all with minimal waiting times. Local authorities are best placed to make choices for their community, which is why we are investing more than £16bn in local government public health services over the current spending period.”