One in six has not discussed sex with their teenage children, yet 90 per cent believe parents should take the lead in sex education.
Just 5 per cent said they ever intended to discuss it. A third of the 2,100 surveyed said they would omit oral sex and 17 per cent would omit masturbation. One in five said children would find out about sex on their own.
The research was commissioned by the sexual health charity Marie Stopes International.