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It is "essential" that action is taken to increase the level and quality of sexual health care provided by family doctors in England, a report says.
Experts evaluating the impact of the National Strategy for Sexual Health, published in 2001, say there has been progress in many areas.
But they say care in England is extremely patchy, with many GPs not offering adequate help to patients.
Doctors said they recognised sexual health as an important part of GP care.
The report, funded by the Department of Health, was written by a team from the Medical Foundation for Aids and Sexual Health for the Independent Advisory Group on Sexual Health.
The wide-ranging report also repeats calls by the advisory group for sex education to be made compulsory.
The report says there has been significant progress in improving access to genitourinary medicine (GUM) clinics, with almost all offering appointments within 48 hours, plus a fall in teenage pregnancy rates - 2006 figures showed them at their lowest rate for 20 years.
But is say there have been worrying increases in the diagnoses of sexually transmitted infections (STIs) and HIV, as well as a rise in demand for abortions.
And it says access to contraceptive services also has to improve, with a wider range of methods offered.
The report stresses it is "essential" that action is taken to increase the level and quality of sexual health care provided by GPs.
Ruth Lowbury, executive director of MEDFASH and a co-author of the report, said: "There are examples of really wonderful practice by family doctors.
"But there are some GPs, we have heard, who haven't really been interested in engaging with sexual health.
"There are differences in basic level of care that people should be able to expect wherever they are.
"We clearly need to provide a mechanism to put in place improvements across the board, rather than the patchy situation we have at the moment."
The system for rewarding GPs for meeting targets, the Quality and Outcomes Framework (QOF) is to be reviewed, and the researchers say sexual health should be included.
"It should be part of the QOF, because that's what provides incentives for GPs."
Deborah Jack, chief executive of the National Aids Trust, said: "If we want to create genuine access to effective local services, we need GPs to be able to identify sexual health needs and be confident talking about sex."
Professor Steve Field, chairman of the Royal College of GPs, said: "They have collected evidence which seems to show that provision of services is patchy.
"But this is a report which comes from a very specialist angle, which doesn't take into account the realities of general practice provision and the work that bodies such as the college have done in sexual health - which we recognise as an important part of GP care."
And he said adding an incentive on sexual health care into the QOF would mean something else would have to come out.
"The best way to improve care is to provide much more integrated services between primary care and specialist clinics."
Public health minister Dawn Primarolo said sexual health would have to continue to be a key priority, both for the NHS and for the government.