Two police officers called out because a woman was "distressed" found themselves having to deliver her baby.
The father-to-be called the police in the early hours from work to say his wife was at home in West Norwood, south east-London, in a distressed state.
PC Matt Spence and PC Gill Moriarty went to the scene not knowing a baby was on the way but helped deliver the girl, who has been named Sara.
The father and ambulance service arrived soon after the birth.
PC Moriarty said: "This was not your usual type of call and it was great to play a part in the birth of a new baby girl."