Health services for children and teenagers, smokers and drug addicts are to be targeted first by the healthcare watchdog under a new ratings system.

The Healthcare Commission said its new "improvement reviews" would focus on areas that could have a major impact on boosting people's well-being in England.

The commission is an independent body which assesses the performance of healthcare organisations and awards annual ratings for each NHS trust in England. It also deals with complaints about the health service and carries out investigations into serious failures.

Star ratings for each health body announced last month were the last before a more patient-centred system is used to assess performance in the coming year.

The first three topics chosen for the new reviews are services for under-18s, the care of problem drug users and efforts to tackle smoking.

Concerns have been raised about the treatment of children and young people in hospital in recent years, including by the inquiry into the Bristol heart babies scandal.

The commission wants to look at what NHS trusts are doing to tailor services to the needs of youngsters, including access to child-specific care in areas such as A&E, on hospital wards and in surgery.

They also want to check that these services are staffed by people properly trained to work with children.

Smoking kills more than 106,000 people each year, and is the single biggest cause of preventable illness and death in the UK. Illnesses caused by smoking cost the NHS at least £1.7bn each year.

The watchdog wants to check what primary care trusts (PCTs) are doing to deliver services to help people stop smoking as well as to reduce exposure to smoking in their area.

Services for drug users will also be assessed with the help of the National Treatment Agency for Substance Misuse (NTA).

There are an estimated 287,000 problem drug users in the UK, with around 160,000 treated for substance misuse in 2004-05.

The reviews will look at how local drug action teams are working to stabilise drug users, for example through prescribing drug alternatives.

In the first instance, the Healthcare Commission will look at the performance of NHS organisations taking part in the review, with each scored on their assessment and these scores fed into the new annual ratings system.

In the second part of the review the commission will develop action plans for around 10% of organisations with the weakest assessments to help them improve their performance.

Strategic health authorities will monitor how organisations implement the action plans.

The review is part of the watchdog's pledge to cut down on the paperwork faced by trusts when they are inspected.

Under the previous programme of so-called "clinical governance reviews", all 572 NHS trusts in England faced an intensive week-long visit by inspectors every three years.

But the improvement reviews will only visit those organisations where improvements are believed to be needed most.

Anna Walker, the chief executive of the Healthcare Commission, said: "Improvement reviews take an in-depth look at an area of national priority in a targeted and proportionate way.

"Feedback we've had from patients and the public has shown that children's health, public health and issues related to mental health are all areas that need attention," she said.

"We look forward to working with those services with most room for improvement to agree action to get their performance in line with the methods and practices of the best."