Her Majesty's Revenue & Customes (HMRC) is to repay an adviser £259,000 for incorrectly charging VAT on intermediary services.
Treasury minister David Gauke has said it is "morally wrong" to pay tradesmen in cash, in the hope of avoiding tax.
Three gang members have been jailed for a total of 35 years for carrying out a £38m VAT fraud through a complex chain of carbon credit trades.
Advisers have been warned not to mislead and confuse HMRC by claiming to offer investment management services - a VAT chargeable activity - while lacking the necessary permissions to do so.
The European Court of Justice (ECJ) has said discretionary portfolio management should not be exempt from VAT.