Local authorities risk incurring huge ongoing billion pound public health costs if they implement cuts to devolved sexual health budgets, experts have warned.

A paper issued jointly today by the Family Planning Association (FPA) and Brook's warns cuts to specialist sexual health services would lead to greater health inequality and expose the public purse to additional £137bn of additional costs.

In addition to greater inequality in services across the country, funding cutback could lead to an increase in unplanned pregnancies and sexually transmitted infections – with knock-on resource implications for local authorities and the NHS, the study warns.

Economic modelling conducted for the charities in their Unreported Nation report suggests the full cost to public services and welfare costs could be as much as £136.7bn. 

This is equivalent of an 8.7% hike in total costs in children's services and treatments should cutbacks worsen as forecast, compared with current funding levels.

According to renowned health think-tank The King's Fund, sexual health will be the main beneficiary of the two-year local authority funding settlement of £2.66bn in 2013/14 and £2.79bn in 2014/15.

Sexual health services, will account annually for almost £650m, followed by adult drug misuse services at almost £570m - together accounting for almost half of all spending.

London councils collectively have allocated the highest proportion of their budgets on sexual health services at 30%, followed by shire counties at around 25%.  The lowest spend on sexual health is among metropolitan and unitary authorities.

FPA acting chief executive, Audrey Simpson, said: ‘It is also imperative that local authorities listen to what people are saying as, now that commissioning structures have changed, they will play a bigger role than ever.

‘Access to the full range of contraceptive methods at a location and time that meets the needs of women is vital to minimise the risk of local inequalities and the consequences of unplanned pregnancy,' Ms Simpson added.

Simon Blake, chief executive of Brook's said: ‘With clear evidence that efficiency savings are already undermining the quality of contraceptive services available today, through location and age-based restrictions, the report predicts a bleak future, should these cuts continue.'

As part of their public campaign to build up a national picture of sexual health, the charities have also launched an interactive online map allowing people across the country to share and rate their own personal experiences of contraceptive services locally.