Family planning services for teenagers do not slow pregnancy rates and may be contributing to a dramatic rise in rates of sexually transmitted infections, research has shown.

Professor David Paton of the Nottingham University Business School claimed on Monday in a speech at the Royal Economic Society annual conference that the government's teenage pregnancy strategy is not delivering.

His findings came in the wake of February's announcement that the latest figures showing an increase in teenage pregnancy rates, following several years of decline.

Since the start of the strategy in 1999, there has been a major expansion of family planning services in the community aimed specifically at young people.

Although teenage pregnancy rates in England have decreased somewhat since 1999, diagnosis rates of sexually transmitted infections have rocketed by 24.3 per cent.

The research also demonstrates that controversial schemes to provide the morning after pill to teenagers free of charge at pharmacists have not reduced teenage conceptions.

In contrast, areas with bigger increases in family planning services have experienced significantly bigger increases in sexually transmitted infections among teenagers.

One explanation for these results is that easier access to family planning for young people may have been partly responsible for the increase in risky sexual behaviour among young people.

"When you introduce policies that seem to be obvious, it is important to factor in the possibility that the policies may actually cause people to change how they behave", said Professor Paton.

"In this case, it appears that some measures aimed at reducing teenage pregnancy rates induced changes in teenage behaviour that were large enough not only to negate the intended impact on conceptions, but to have an adverse impact on another important area of sexual health - sexually transmitted infections."