Initial warnings from the whistleblower who revealed a £250m profit overstatement at Tesco were ignored, it is understood.

Concerns were first flagged before former chief executive Philip Clarke left the retailer in July after a profit warning, according to the Sunday Times.

The whistleblower, an accountant who reported into UK finance director Carl Rogberg, raised concerns but “failed to get traction”, a senior source at Tesco said.

The accountant then tried again after new chief executive Dave Lewis took the helm at the beginning of the month, passing the information on to Tesco’s general counsel, alerting Lewis on September 19.

This led to Tesco revealing the overstatement on Monday September 22. The grocer has launched an investigation into the error and suspended four senior executives in the wake of the scandal.

Tesco declined to comment.

The investigation is thought to focus on the culture of the grocer, as there are concerns that managers may have been pressured into using improper practices.

Tesco’s international division is also being examined to see if issues are more widespread, according to the Times.

The Mail on Sunday also reported staff had been ordered not to shred or delete documents while an investigation into the scandal takes place.

In addition, Tesco pulled a £3bn refinancing arrangement two days before disclosing the £250m overstatement, the Financial Times reported. The grocer had been due to sign up 15 banks a week ago for a £3bn revolving credit facility.