The initiative began in Oxford and was recently extended to Derby following a £69,712 grant from the Big Lottery Fund.
Citizens Advice, which relies on trained volunteers to provide free and confidential advice on issues such as personal finance, benefits and housing, partnered with Sudbury Open Prison to train low-risk prisoners as advisers in Derby.
Local residents expressed fears in the local media that giving prisoners access to information on clients' finances and contact details could put people at risk, particularly the elderly.
The city council added its voice to the criticism and claimed the scheme damages public confidence in Citizens Advice.
But Citizens Advice argued that the scheme allows bureaux to deal with more enquiries and expand their services to the public while contributing to reducing the risk of prisoners reoffending.
"We are obviously aware of our responsibilities as an organisation to manage this initiative in a way that puts our clients' interests first," said a spokesman from the organisation. "Our prime concerns remain providing a top quality free, independent advice service to the public, and safeguarding the interests of our clients."
Derby Citizens Advice Bureau hopes that the scheme will enable it to take an extra 17,000 calls over three years, and to extend their opening hours to include evenings and weekends. The selection and training of prisoners will begin this autumn.
The bureau also stressed that, in Oxford, where the scheme has been running for two years, there have been no complaints.
This autumn, project funder the Esmee Fairbairn Foundation will publish a report that the charity will use to decide how the scheme should be extended.