Access to sexual health and HIV services has been dramatically reduced following changes to the funding and organisation of the services, health leaders have warned.
The British Association of Sexual Health and HIV (BASHH) and the British HIV Association (BHIVA) said surveys of their members show the sector is at "breaking point".
The majority (92%) of respondents to a survey of BASHH members said they were worried, or extremely worried, about the future delivery of sexual health care in England.
More than half (54%) reported decreases in the overall level of service access to patients over the past year, with a further 16% saying that access had significantly decreased.
A parallel poll of members of BHIVA found more than three-quarters (76%) felt that care delivered to patients in their HIV service had worsened.
And they warned that, with Public Health England (PHE) data showing a 13% increase in attendance of sexual health services between 2013 and 2017, budgetary pressure means that this demand cannot always be met, with more patients now either turned away or redirected to other parts of the health system.
Six in 10 (63%) BASHH respondents said they had to turn away patients each week, while both surveys revealed significant reductions in services such as the delivery of HIV prevention activities, outreach to vulnerable populations, and cervical screening.
Three-quarters of BHIVA members (75%) said that there had been an impact on access to HIV prevention advice and condoms, with 63% saying access had been reduced and 44% of BASHH members reporting that HIV prevention services had decreased.
Four out of 10 (41%) BHIVA members said access to sexual health screening had been reduced, despite HIV positive people being at greater overall risk of sexually transmitted infections.
It also showed that it is becoming more difficult for people to test for HIV, with more than a third (35%) of respondents reporting that there is now reduced access to testing in their own location.
At the same time, more than a third (34%) of BHIVA respondents and 32% of BASHH respondents reported decreased provision of reproductive health and contraception.
BASHH president Dr Olwen Williams (pictured) said: "Providing high-quality free and open-access care for all those that need it has been the bedrock of sexual health in this country for over a century.
"Whilst we are doing our utmost to maintain standards in the face of record demand and dramatic increases in infections, such as syphilis and gonorrhoea in recent years, these surveys clearly show that continued cuts to funding are taking their toll.
"Current levels of sexual health funding are quite simply not sustainable and the pressures they are generating are having a seriously detrimental impact on the morale and wellbeing of staff.
"Without increased support to match the huge growth in demand, the consequences will likely be disastrous for individuals and our public health as a whole."
BHIVA chairwoman Professor Chloe Orkin said: "Despite the stated ambition of policy makers to reduce health inequalities this will not be possible without robustly funded, sustainable services.
"Our survey results provide clear evidence that we need to upgrade, not reduce, services if we are to support and protect vulnerable populations.
"We have made huge strides in the control of HIV, so it is particularly worrying to see that important aspects of HIV care, such as access to prevention services, testing and mental health support, have been reduced."
A Department of Health and Social Care spokesman said: "We have a strong track record on sexual health with teenage pregnancies at an all-time low and sexually transmitted infections continuing to fall.
"Sexual health services and tests are now more widely available online, which means people can get tested at a time that suits them - over 11,000 diagnoses from online tests were reported last year.
"We are giving £16 billion to local authorities for public health services over the current spending period, as they are best placed to understand and meet the public health needs of their local communities."
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