There are concerns that men who are "clearly kerb crawlers" are not being charged and convicted, due to what is regarded as a lack of sufficient evidence, an MSP has warned.

Legislation that criminalised soliciting of a prostitute for sex and loitering for the same purpose came into force in 2007. Revised guidelines for enforcing the law were issued last year.

During a session on justice issues at Holyrood, Labour MSP Malcolm Chisholm questioned whether Solicitor General Lesley Thomson was satisfied with the criteria of evidence required to secure convictions for those who attempt to pick up prostitutes.

He said: "(Ms Thomson) will be aware of some of the concerns of my constituents that men who are clearly kerb crawlers are not being charged and convicted because of a lack of what is regarded as sufficiency of evidence. I wonder if the Solicitor General is satisfied with the criteria for sufficiency of evidence with regard to kerb crawling."

Ms Thomson told the chamber there were 77 convictions for kerb crawling under the Prostitution (Public Places) (Scotland) Act in 2011.

Every successful prosecution, Ms Thomson said, required sufficient corroborated evidence. "There are no differences in relation to the understanding of evidential requirements," she said. "For the avoidance of doubt, those evidential requirements can include direct evidence – eye witness accounts from police and civilians, admissions in interview, or circumstantial evidence from which inferences can be drawn."