Investigators in France have revealed the lengths that they went to protect data during its probe into Google's tax payments.

The lead investigator Eliane Houlette said that the investigation, which was code-named Operation Tulip, banned all internet use and only used one word-processor.

Her team was also not allowed to say 'Google' - referring to it as Tulip instead.

"We decided to never utter the word 'Google,' to give the firm another name ... we worked on this case fully offline for nearly a year," Ms Houlette told French radio station Europe1.

She added that a special emphasis was put on avoiding leaks, "given the activities of the company."

The raid was carried out in the early hours of Tuesday, May 24th - and it involved almost 100 investigators.

France is seeking €1.6bn in back taxes from Google, a finance ministry source said earlier in this year.

The action was part of a preliminary criminal investigation which opened in June 2015.

French finance minister, Michel Sapin has warned that the country will do all that it can to ensure that multinationals operating in France pay their full tax bills.

The minister has ruled out negotiating a deal with Google if it is found to owe back-taxes.

This investigation has focused on taxes on Google’s activities in France being paid by its European headquarters in Dublin.

Google says that it complies fully with French tax law.