The employee, who has not been named, reportedly drank nine glasses of beer during a five-hour-long night out with co-workers in Yokohama on 6 February.

Local media said that he did not realise he had lost his bag until after he got off his train ride home in another city, Sumida.

The finance ministry has said it was “deeply sorry” for the incident that “significantly undermined public trust”, according to public broadcaster NHK.

The bag had contained documents which had the names and addresses of 187 suspected drug smugglers and recipients of marijuana seeds, the ministry said.

It had also contained business laptops with the employee’s personal data.

The employee, who is assigned to the customs and tariff bureau, was not named in the NHK report.

The BBC has reached out to the finance ministry for comment on Tuesday, a public holiday in Japan.

Alcohol has long been seen as a social lubricant for thousands of years in Japan, where business deals and difficult issues are discussed over bottles of beer and sake.

It is believed that drinking alcohol creates a more relaxed environment for such discussions.