The term “false economy” is bandied about a lot in discussions about government cuts, but when it comes to slashing public health budgets it is entirely appropriate. Think for one moment about the point of preventative public health services, such as sexual health clinics, suicide prevention schemes and smoking cessation programmes – to avert serious problems and crises later on – and it really isn’t difficult to join the dots.

Reducing or cutting initiatives that help keep people out of doctors’ surgeries and hospitals stores up future problems for an already stretched NHS, yet this is exactly what is happening.

As a coalition of health and local authority organisations warned last month in a letter to the chancellor, slicing 6.2% of public health funding used for “vital” locally provided services completely undermines pledges to pump billions into the NHS by 2020. Factor in calculations from the Faculty of Public Health (FPH) that the impact down the line for the NHS could be more than £1bn in additional costs and the folly of sacrificing prevention becomes all too clear on both economic and health grounds.

With the Treasury likely to chop even more by 2020 on top of the £200m already shaved off this year’s budgets this is no time for complacency. There is considerable evidence for the return on investment in public health intervention yet all kinds of crucial services are potentially under threat. The scale of the ramifications for health inequalities [pdf] and the health service are already beginning to emerge.

For example, when councils across the country were surveyed recently by the FPH, 77% said they expected obesity interventions to be cut – despite illnesses related to excess weight being one of the biggest and fastest growing financial strains on the health service.

The same survey found that 61% of local authorities anticipated additional cuts to sexual health services. Sexual health is an interesting case in point on the incontrovertible connection between how cuts in one area impact another. Many services are aimed at young, vulnerable people who if reached early enough can avoid a morass of complex problems from, for example, STIs. But, if they don’t have access to prevention they are more likely to need treatment and care which will cost the NHS dear.

Concerns have been raised in particular about recent increases in STIs. In its submission to the Treasury prior to the spending review, sexual health organisation Brook cautioned that if these trends continue, combined with expected “worsened access to services”, total spend on STIs by 2020 could top £6bn.

According to Office for National Statistic figures for the second quarter of 2015, teenage pregnancies rose on the previous year by 1.2% in the north-east and 2.8% in the north-west. Declines in births to teenage mothers were heralded a public health success story in the wake of the 1999 Teenage Pregnancy Strategy, which led to record low rates. Nationally the rate continues its decline, but if fractures are beginning to show they cannot be ignored.

Brook’s chief executive Jules Hillier says it is important that the wider impact of cuts is understood. “The Department of Health itself quotes [pdf] the finding that every £1 spent on contraception saves £11 in other healthcare costs, meaning the recent, devastating cuts to the sexual health sector are economically nonsensical as well as hugely damaging to the nation’s health and wellbeing.”In a report [pdf] published last week the Family Planning Association, which says it has already seen evidence of restrictions to local authorities services across the country, made some stark projections. Based on what it says is a conservative estimate of a 10% reduction in access to services by 2020, the overall cost of STIs and unintended pregnancies could exceed £77bn between now and then. This would include £8.6bn of additional public sector costs “health and non-health”.

It concludes: “If the cuts to public health spending already announced become the norm over the next five years, every £1 of expenditure cut could cost as much as £86 further down the line.”

The impact of cuts imposed on sexual health and other preventative services will take time to fully manifest. But make no mistake, they will be sharply felt – and come at great price both financially and in terms of the UK health.

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• This article was amended on 18 February 2016. An earlier version misnamed Jules Hillier as Judith.