An accountant who defrauded HM Revenue and Customs (HMRC) of more than £2m by misadvising and defrauding his clients has been jailed for seven years.
Simon Terry Pearce, 48, understated his clients' earnings and overstated their expenses in order to cut tax bills, Truro Crown Court heard.
He also kept cash from tax rebates to his clients, the court was told.
Pearce, from Truro in Cornwall, was found guilty of 26 offences, including fraud and cheating HMRC.
After complaints from clients, HMRC launched inquiries in 2010 into tax returns Pearce had made on behalf of his customers while trading under the name ST Pearce, based in Duke Street, St Austell.
From 2010 until November 2012, when he was charged, inquiries found his clients owed £1.3m in unpaid tax as a result of Pearce's work.
Another investigation concluded about another £750,000 went unpaid between 2006 and 2009.
HMRC investigators also said Pearce also claimed tax repayments on behalf of some clients but failed to pass on some or all of the money.
Twenty-seven witnesses gave evidence in the 10-week trial, with some telling the court of having to remortgage homes to pay what they owed as a result of Pearce's advice.
Prosecutors said his crimes had a "devastating effect on their lives".
Pearce, of Trafalgar Road, was found guilty on Tuesday of charges including fraudulently using his position as an accountant, false representation and cheating HMRC.
Sentencing him on Wednesday, Judge John Neligan condemned what he said was "persistent" cheating.
He told Pearce he had "demonstrated a systematically dishonest approach to tax returns".
After sentencing, HMRC said the case was "believed to be Cornwall's largest tax fraud trial".
Colin Spinks, of HMRC, said: "Honest, hardworking people trusted Pearce with their finances, but he put their livelihoods at risk through his own greed."