Parent company mm O2 is to close the mobile phone network's office in Hammersmith, London, which has housed the central marketing team, product teams and some support functions of the group, including HR and legal.
The closure is likely to lead to up to 200 redundancies and will save up to £45m each year. O2 is going through a consultation process with its staff.
It is not known how many marketers will be affected by the redundancies, although O2 has confirmed that it will not replace Will Harris, its former vice-president of brand marketing, who last week joined the Conservative Party as marketing director.
He is expected to continue to work on a consultancy basis for O2 in the short-term.
The future of Anna Russell, O2 's head of brand, who took on Harris' responsibilities when he went on his six-month sabbatical in June (Marketing June 19), is also unclear, but it is thought that she has been offered a senior UK role.
The central marketing team will be replaced by a brand executive committee, which will have representatives from each of O2's territories and from its creative and branding agencies: Vallance Carruthers Coleman Priest and Lambie Nairn.
O2 UK marketing director Cath Keers is tipped to lead the committee, which will ensure that O2 is putting out a consistent brand and advertising message.
An O2 spokesman said the changes were being made to give each territory "more operating control and to ensure that we are quicker to market".
The decision comes as O2 looks to establish a niche for itself in offering unique mobile devices such as its mobile music player, which launched last week in partnership with record labels including BMG and Warner.