Metro Bank has been fined £16.6 million by regulators for failings over money laundering controls from 2016 to 2020.

The issues, which continued for four years despite concerns being raised by junior staff, applied to more than 60 million transactions with a value of more than £51 billion, according to the Financial Conduct Authority (FCA).

The watchdog said Metro Bank automated financial crime monitoring in 2016 but its system “did not work as intended”.

Metro’s failings risked a gap being left in our defence against the criminal misuse of our financial system. Those failings went on for too long

An error in how data went into the system meant transactions on the same day an account opened along with many further transactions “were not monitored”.

Junior staff raised concerns about the issue in 2017 and 2018 “but these did not result in the issue being identified and fixed”.

Metro Bank put a fix in place in July 2019 but even then did not have a system to consistently check that all relevant transactions were being monitored correctly until December 2020.

Therese Chambers, joint executive director of enforcement and market oversight at the FCA, said: “Metro’s failings risked a gap being left in our defence against the criminal misuse of our financial system. Those failings went on for too long.”

The company would have been fined £23.8 million but it agreed to resolve the matters and so qualified for a 30% discount, the watchdog said.

Metro Bank has about three million customers in the UK and earlier this year announced a round of heavy cost-cutting which saw it axe 1,000 jobs.

The company said on Tuesday that it returned to profitability in October amid what chief executive Daniel Frumkin called “strong progress”.

He added that the turnaround was “thanks to our continued emphasis on cost discipline and balance sheet management”.

He said the bank had “positive momentum moving forward, with strong cost control and a robust pipeline supporting our pivot towards higher yielding commercial, corporate, SME and specialist mortgages”.