Illegal car traders operating at roadside venues and car fairs are slipping through the Government's net, according to the Motor Trade Association.
In the past month six people were convicted of illegal vehicle trading, but MTA warns the figure could be much higher.
MTA spokesman Tony Everett said while the increase in prosecutions was welcome, it still only represented a small portion of those who operated outside of the law.
"Each year, roughly 450,000 cars change hands between private sellers. Given the size of the market, it is likely the number of illegal traders operating is considerably larger than MBIE's figures indicate."
Many illegal traders operating at roadside sales venues and car fairs were slipping past the attention of government agencies, he said.