The next generation of adults is likely to be the fattest, most mentally disturbed and least fertile in history, doctors warned yesterday.

Teenagers who gorge on fast food, binge on alcohol and drugs, and indulge in promiscuous sex represent a public-health time bomb that could overwhelm the NHS, the British Medical Association (BMA) said. One fifth of youngsters aged 13 to 16 are overweight and a quarter of those aged 16 to 19 smoke at least once a week. British adolescents are drinking more than ever, and have one of the highest levels of alcohol use in Europe.

Their sexual health is also suffering, with as many as one in 10 girls aged 16 to 19 infected with chlamydia, a sexually-transmitted disease which can make sufferers infertile.

The BMA, in a report on adolescent health, called on the Government to put more money into services which specifically target adolescents, who, the association said,were stuck in a "no man's land" between child and adult health services.

Dr Russell Viner, consultant in adolescent medicine at University College Hospitals and Great Ormond Street Hospital, said the lack of services dedicated to young people in Britain was a "scandal".

He said: "The next generation will be the most infertile and the most obese in the history of mankind and it might also have the worst mental health." Dr Vivienne Nathanson, head of science and ethics at the BMA, said teenagers' behaviour posed "an extraordinary threat to an entire generation". She said: "It is also a threat to all of us. How can the NHS be funded to deal with that kind of health crisis? We can't expect young people to think that far into the future. We have to do some of the thinking for them."

The report calls for a "joined-up" approach by government departments and agencies to deal with the problems, saying there should be more education on sex, drugs and diet in schools, as well as outside through awareness campaigns and parental guidance. Dr Nathanson said the current provision of sexual health services in Britain was "woefully inadequate" and something needed to be done to make clinics more accessible to young people. She said: "Access to services is key. Do we really expect a 15-year-old boy with gonorrhoea to take time off school to visit his GP and talk about his sex life?"