Research by the Legal Aid Board (LAB) and the Law Society has found that although there have been "measurable and significant improvements in the quality of police station legal advice", many advisers still do not measure up to the LAB's standards.
The LAB's accreditation scheme was introduced in 1995 after concerns were expressed about the quality of advice given by solicitors' representatives.
During the first year, only a quarter successfully passed through the 12-month monitoring period required to achieve full accreditation, and the numbers have increased only slightly since then. More than 1,600 people have gained full accreditation so far.
One of the report's recommendations is to enhance the LAB's abilities to monitor solicitors supervising probationary representatives who fail to become accredited.
It also concludes that the way in which duty solicitors are selected will need to be reviewed. It adds that because of continuing low standards, consideration should be given to requiring all solicitors giving such advice either to be duty solicitors or to become accredited.
Brian Spiro, a partner at Simons Muirhead & Burton and co-editor of the Police Station Adviser's Index, said that, although he did not object to the scheme, quality would always be variable as long as the government was not prepared to fund qualified solicitors to give advice to every suspect in police stations.