A recent survey suggests that the public suffers a worrying lack of knowledge and understanding about sex, with confusion and misunderstandings over contraception in particular.

The Family Planning Association (FPA), who led the survey, found some people to believe that exercise or urinating after intercourse could prevent pregnancy.

The FPA said better sex education was needed, with researchers at Coventry University calling for lessons to be tailored to pupils' sexual experience. The Government said it was up to teachers to decide on sex education.

Although all secondary schools are required to include sex education as part of their teaching programme, there are no rules over the content, leading to complaints that lessons are too biological.

On sex education, only four per cent said their experience at school was excellent, 38 per cent described it as poor and 18 per cent said they did not get any.

The FPA survey, published to coincide with the start of Contraceptive Awareness Week, found that half of people did not know when was the most fertile point of a woman's menstrual cycle, while the majority of those questioned gave the wrong answer or didn't know it is possible for sperm to live inside a woman's body for up to seven days.

Anne Weyman, chief executive of the FPA, said: "This survey exposes how far the current system of providing sex education is failing and also that people are acutely aware that it is letting them down.

"Reproductive biology is the only statutory part of the national curriculum and even this isn't achieving acceptable standards."

For Contraception Awareness Week posters have been sent to 2,000 health and other professionals across the country.