Businesses that are not registered to pay tax will come under closer scrutiny by Revenue & Customs as the taxman seeks to claw back the estimated £2bn lost each year, Grant Thornton says. White collar professionals have been found to be among the millions of workers estimated to be taking part in the hidden economy as the downturn sets in, according to a report published by the Commons' Public Accounts Committee. Tax investigations director at Grant Thornton Gary Ashford, said: 'Everyone working in professions where there is scope to be paid cash in hand or carry on second jobs should review their affairs and be proactive in declaring any discrepancies to the taxman.'