The survey, published this week by sexual health charity the Terrence Higgins Trust, shows that patients trying to access GUM services are least likely to get an appointment within the government's 48-hour target in December and over the Christmas period.
Only 36 per cent of GUM clinics were able to offer patients an appointment within 48 hours during December.
Trust chief executive Nick Partridge said: 'It's not just where you live, but when you try to get an appointment that affects your chance of being seen within 48 hours. This lack of consistency is bad for patients, and bad for clinic staff, too.'
Mr Partridge said that funding for GUM services was often being 'diverted elsewhere'.
'We must ring-fence money for sexual health if we're going to see this picture improved,' he added.
Further findings from the report showed that it consistently took more than three calls to get through to around 20 per cent of clinics, and that around 30 per cent of people with symptomatic sexually transmitted infections continued to have sex while they waited for an appointment, a key factor in rising infection rates.
There was also a marked increase in access to walk-in only clinics rising from 3 per cent of the total number of consultations to 9 per cent over the six months in which the survey was conducted.