SINGAPORE - A former construction surveyor whose one-man moneylending racket was uncovered by a routine police check has been jailed for 3 1/2 years and fined $450,000.

Malaysian Looi Teck Hock had been running the business since 2006 but was caught in 2017 when officers screened him at Hougang MRT station and found four bank cards belonging to other men.

Looi, a permanent resident, was arrested after failing to account for how he ended up with the cards.

He was later charged with 122 counts of carrying on the business of an unlicensed moneylender involving at least 83 debtors. The Straits Times understands that this was the most number of charges and debtors for a one-man operation.

Looi, 47, pleaded guilty to 15 of the charges and the remaining 107 were considered during sentencing.

His scale of offending was "virtually unprecedented", said District Judge Marvin Bay on Wednesday (Feb 20).

Deputy Public Prosecutor Dwayne Lum told the court that Looi began moneylending in 2006 while working as a construction surveyor as he wanted to earn extra cash.

He initially targeted Thai and Indian foreign construction workers at his company. As the business grew, he would tell them to inform other foreign workers about his services.

DPP Lum said: "The accused would loan money to these foreign workers in cash by hand, or via funds transfer.

"The accused would charge an interest of 10 per cent per month. The debtors would be expected to pay ... until the principal loan amount was cleared."

Looi made his customers surrender their ATM cards and their PINs . He would then withdraw the repayment amount when the foreign workers received their salaries in their accounts.

After deducting the amounts owed, Looi gave the debtors the rest of their pay.

Looi was retrenched in 2015 but did not bother searching for another job as he regarded his unlicensed moneylending as an "easy profit-making business idea".

The business grew gradually and by the time he was arrested on Aug 10, 2017, he was making annual profits of $30,000 to $40,000 or $3,000 or so a month. )

Judge Bay said on Wednesday that Looi had "exploited a vulnerable class of persons".

He added: "Mr Looi's imposition of exorbitant ... interest on relatively modest sums extended would keep these migrant workers in an extended state of penury and desperation."

First-time offenders convicted of carrying on the business of an unlicensed moneylender can be jailed for up to four years and fined between $30,000 and $300,000 for each charge.

Looi will have to spend an additional 11 months and a week behind bars if he is unable to pay the $450,000 fine.