An investigation by the Revenue Commissioners into businesses paid in cash yielded tens of millions of euro in the first eight months of this year.

RTÉ News has learned the inquiry - the Shadow Economy Project - looked at several industries, ranging from building firms to scrap metal merchants to landlords and nursing homes.

Almost €82m was recouped by tax inspectors between January and August last.

The biggest amount came from landlords, who had to pay €21m.

White collar cash accounted for €16.5m, which includes cash payments to doctors, dentists, vets, solicitors, accountants, physiotherapists and teachers giving grinds.

Around €17m was paid back from those working in construction.

Couriers had to pay €2m and the security industry €5m.

Nursing homes had a bill of €730,000 and €220,000 was recovered from those selling scrap metal.

Garages handed over €460,000, while the cash-for-gold sector has so far yielded €55,000.