The first episode of the second series focuses on Britain's sexual health. In just ten years the number of diagnosed new cases of sexually transmitted infections has doubled and sexual health services account for over £1billion of the NHS budget. Lead consultant Rachael Jones and her team at the West London Centre for Sexual Health are tackling this sexual time bomb. Chlamydia is the clinic's number one diagnosis. But Michael, 25, is dismissive: 'I thought everyone gets it. If you haven't had it, you're boring. It's almost like being brought into manhood,' he says. And many in this generation don't use condoms, routinely taking risks. As 19-year-old Stacey says, 'if I have to put one on I'll put on one. If she's ok with it, I won't.' Undetected and untreated, STIs can lead to infertility, cancer and even death. Yet staff at the clinic are not only coping with high numbers of patients, but also spend much of their time trying to make their young patients realise the dangers of STIs and the importance of practicing safe sex. The clinic runs a confidential after-school walk-in service for under-19s, but staff must work quickly as patients often get bored and do not want to wait. Despite a recent miscarriage, 15-year-old Shannon is not taking her pill and misses appointments to have her contraceptive implant - a key weapon in the government's multi-million pound campaign to halve teen pregnancy - fitted, forcing a sexual health support worker to take her to the op. And, in three years, Dr Rachael Jones has seen the sudden spread of HIV amongst teenagers. Perry, 17, who has had five HIV screenings in one year, chillingly says: 'If I do have HIV it would be a bit upsetting but I'd have to live with. You can't cry forever.'