Devon County Council has defended the number of criminal background checks it carried out last year.
According to the Manifesto Club - which campaigns against over-regulation - the council authorised 20,095 checks in 2010-11.
It said nearly one million checks were done by councils in England and Wales - 24% of which were for voluntary jobs.
But Devon County Council said the issue of safety and welfare had to be taken "extremely seriously".
'Provide the service'
"We have to ensure that the right checks are carried out prior to filling certain posts," a statement from the council said.
"Devon's figure is proportionally higher because we act as an umbrella agency and provide the service for a number of organisations such as charities, external companies, schools, academies and district councils."
The Manifesto Club, which compiled its report using Freedom of Information requests, said with each check costing nearly £50, the total spent last year was nearly £45m.
The only councils which carried out more checks than Devon County were Hertfordshire (21,680) and Essex (21,610).
In the rest of the South West, Cornwall Council authorised 9,270 checks, while Plymouth City Council carried out 7,499. Torbay Council has its checks done by Devon County Council.
The club said vetting was carried out for positions including parent volunteers, burger van sellers and foreign exchange hosts.
Manifesto Club Spokeswoman Josie Appleton said: "I'm not against vetting per se (in itself), but the number being carried out by some councils now is out of proportion."
The club said it would submit its data to the Criminal Record Bureau and ask it to investigate authorities' vetting practice.
The Home Office - which is responsible for the bureau - said the report highlighted how excessive the current system had become.
"This is why we are scaling the regime back to common-sense levels so that the public are properly protected but the number of unnecessary checks is substantially reduced."