The research, commissioned by children's charity Plan International UK, found that 85 per cent of those polled think that SRE should be mandatory in state schools and 82 per cent agreeing that it should also be compulsory at faith schools.
But the survey, conducted among 2007 adults, also found that of those who received SRE at school, only 27 per cent found the classes informative.
The research comes as the Government faces pressure to make sex education mandatory to combat sexual harassment and abuse.
Tanya Barron, Plan International UK's chief executive, said: "Girls are telling us that they are suffering harassment at school, they don't feel safe online and are scared on the street.
"They are telling us unequivocally that mandatory and good-quality sex and relationships education is one of the most important ways to help change this situation."
Under the current national curriculum SRE is compulsory from age 11 in state-funded secondary schools, but parents can choose to remove their children from the lessons if they wish.
A Department for Education spokeswoman said: "High-quality education on sex and relationships is a vital part of preparing young people for success in adult life - helping them make informed choices, stay safe and learn to respect themselves and others.
"We are actively considering what further steps we could take to improve the quality and accessibility of sex and relationships education."