PC Scott Johnson admitted having sexual relationship with vulnerable woman
PC Scott Johnson, 45, met the victim, who cannot be named, while he was on duty with the Met Police in September 2016
The relationship continued until October last year, when he was arrested.
Johnson pleaded guilty at Southwark Crown Court to misconduct in public office.
The Independent reports that Prosecutor Alexandra Felix said the relationship was carried out over a "protracted period of time" and that the officer sent naked photographs of himself to the victim.
Judge Martin Beddoe adjourned sentencing until 12 November but warned Mr Johnson that he is likely to face custody.
"You must be under no illusion that the offence to which you have pleaded guilty is very serious - it crosses the custody threshold, in my view, by a large margin," he said.
"And the presumption must be that you will be sent to prison; you must not think that because I have renewed bail and ordered a pre-sentence report that is any indication of what will happen on November 12."
Richard Atchley, defending, said Mr Johnson accepted that his behaviour was "strange to say the least".
He said the officer had just gone through a separation and that "his mother had died in an accident and he was not in a good place."
He added that Mr Johnson is suffering from depression and is the sole carer for his father, who has cancer.
Johnson, who worked in the London borough of Hammersmith and Fulham, has also been suspended from duty.
October 12, 2018