HIV transmissions among gay and bisexual men have dropped 73% since 2014, according to figures from Public Health England.
The decline has been credited to the introduction of the pre-exposure prophylaxis (PrEP) pill, which is freely available in Scotland and Wales to people at high risk of HIV exposure.
There is less access to the pill in England, where people are required to enrol in a trial which began in 2017.
At least 15 people are known to have contracted HIV while on the waiting list for PrEP.
Clinical trials have shown PrEP to be most effective when taken in two particular ways, one regularly every day, or in larger doses before and after having sex.
It is believed that both methods, when correctly followed, are almost 100% effective at preventing transmission.
The drug is primarily targeted at men who have unprotected sex with other men, as well as people whose partners have HIV.
It is not used by those who already have HIV, who receive different treatments.
Transmission of the virus has plummeted since 2014, when the new figures begin, and are down from 2,300 to just 800 in 2018.
According to Public Health England's data, 93% of the estimated 103,800 people in the UK living with HIV have been diagnosed, and 97% of those are receiving treatment which suppresses the virus.
Health Secretary Matt Hancock said last year that he wanted the UK to reach a transmission rate of zero by 2030.
Campaigners have called for PrEP to more widely available.
Phil Samba, a PrEP user and member of campaign group Prepster, said the figures showed how effective PrEP and rapid access to HIV testing and treatment was.
Mr Samba said the government should "get a grip and fund a full PrEP service now."