A proposed crackdown on tax-dodging by builders would penalise the genuinely self-employed, boost the black economy and increase construction costs, according to critics lining up to oppose the latest of numerous initiatives aimed at tackling “bogus” self-employment.

As the Treasury considers tax changes for the pre-Budget report expected in December, it is facing a mounting backlash against proposals outlined in a recent consultation document to collect an extra £350m of tax and national insurance contributions from an estimated 300,000 workers falsely described as self-employed . However, it has said it would delay the measures until the industry has recovered from the recession.