While hacking and corruption carry prison terms, the offence of perverting the course of justice carries a maximum life sentence.
Of the 29 arrests in Operation Weeting and 23 in Operation Elveden, only three people prior to the six held yesterday have been arrested on suspicion of conspiracy to pervert the course of justice.
Previously only Glenn Mulcaire, the private investigator, Ross Hall, a former reporter at the News of the World and Cheryl Carter, the former personal assistant to Rebekah Brooks, have been held under the offence.
Yesterday's arrests could be interpreted as a new stage in the investigation by Scotland Yard.
The bulk of the initial arrests concentrated on phone hacking. More recently arrests have focussed on journalists, particularly on the Sun newspaper, who are alleged to have paid public officials in exchange for information.
That all of yesterday's arrests were on suspicion of conspiracy to pervert the course of justice suggests that the Metropolitan Police are now turning their attentions to those they suspect may have been involved in a cover-up.