There have only been seven prosecutions of illegal taxis in Coleraine and Limavady in the past three years despite 3,331 inspections by DVA enforcement officers.
The figures were revealed in an Assembly answer by Mark H Durkan, the Minister of Environment, following a written question on the issue by East Londonderry SDLP member, John Dallat.
Mr Durkan said that in Coleraine from April 2011 to March 2014 there were six prosecutions with just one in Limavady.
Enforcement officers carried out a total of 232 inspections in Coleraine, the DoE figures showed, issuing 12 fixed penalties, eight prohibition notices and 32 defect notices.
In Limavady 101 inspections were carried out with seven fixed penalties issues as well as eight prohibitions notices and 21 defect notices.
A prohibition notice is issued where one or more serious defects are identified in order to restrict the continued use of the offending vehicle on a road.
A defect notice is issued where minor defects are identified and requires the owner of the vehicle to present it at a Vehicle Testing Centre within 14 days for further inspection.