The Healthcare Commission has pledged to act faster when investigating serious failures at trusts.

The regulator said it needed to "spot issues earlier and move more quickly" in a report on its own performance since it was established in 2004.

It will also use more "rapid interventions" - like its recent probe into mortality rates following heart surgery at Papworth Hospital - instead of full-scale investigations.

The report Making a difference? draws together findings from a series of independent evaluations of the regulator's work.

The commission said these showed it had "made a deep impact on the health and healthcare of patients" and that the annual health check was "a clear catalyst for change".

However, it acknowledged there was room for improvement. This included its approach to investigating serious problems at individual organisations.

It said better use of data such as high mortality rates was needed to identify and follow up potential problems and ensure lessons were spread more widely.

The watchdog also promised to work harder to boost confidence in the annual health check after one in five trusts said it was not a fair reflection of their performance.

"There is evidence of frustration with the significant amount of duplication and overlap with the work of other regulators, concerns and confusion about follow-up inspections and worries about compatibility of scores across trusts," said the report.

Trusts were also concerned about the amount of work involved while a lack of clarity about the scoring process may have added to dissatisfaction, it added.

A Healthcare Commission spokeswoman said trust feedback had informed plans for the 2008-09 health check and the body had been working to boost understanding of the two-year-old system.

"Most trusts believe the benefits far outweigh the costs and that it has led to improvements in clinical quality, care and safety," she said.

She said all lessons the commission had learned over the past four years would help inform plans for the new healthcare regulator, the Care Quality Commission.

NHS Confederation policy director Nigel Edwards said that trusts were anxious about the change as the new body was an "unknown quantity".

"New organisations want to prove themselves and we will be watching very carefully what it does," he said.