The most worrying failures identified involved Disclosure Scotland checks (which provide information on criminal convictions and investigations) not being done and employers not verifying employees' fitness to do the job.

Marcia Ramsay, acting director of the Care Commission's Adult Services Regulation, said: "People who use services, their families and carers want to know that the many organisations that provide care take recruitment seriously.

"People using care services can be very vulnerable, so it's particularly important to be thorough - check references and qualifications and do disclosure checks.

"We found that the large majority were recruiting in a safe and effective manner, but a significant minority, of just over one in five services, need to improve."

Ramsay added: "Care providers must provide the high quality of care set out in Scotland's National Care Standards. Their ability to do so relies on recruiting the right staff. This report sets a benchmark on recruitment practices which we can use when we conduct another review in the near future.

"We will continue to follow up on those services where improvement was needed and encourage everyone involved to ensure recruitment into this vital sector is done properly. Indeed, I'm happy to report that this report ensured a number of care services improved their practices immediately and have ensured best practice is put in place for the future."

The findings are revealed in the Safer Recruitment for Safer Services report, based on a review of nearly 4500 of Scotland's care services over a two-year period.

It was conducted following concerns of the Care Commission and the Scottish Social Services Council over recruitment procedures.

Carole Wilkinson, chief executive of the Scottish Social Services Council, added: "The SSSC Code of Practice for Employers of Social Service Workers is clear that employers must use rigorous and thorough recruitment and selection processes, making sure that only people who have the right knowledge and skills and who are suitable to provide social services are allowed to enter the workforce.

"It is reassuring that the majority of service providers are meeting safe recruitment requirements but as the report shows there is still work to be done. We will continue to work closely with the Care Commission to make sure employers are aware of their responsibilities."

Public health minister Shona Robison told BBC Radio Scotland: "The important thing is that people who are receiving care services and their families need to be reassured that those providing the care take recruitment seriously, given that those using care services are quite often very vulnerable."

Ms Robison said the Care Commission had reported a number of services had already put improvements in place.

She added: "They have found weaknesses in some of the care providers, they have been very clear that those care providers have to improve and they are saying that they are pleased with the progress that those care providers have made."

Another set of inspections into the care service recruitment system are expected to be carried out next year.