Land Securities, the landlord, has appointed Ocean "to build on the long-term heritage" of the famous outdoor site by turning it into "an innovative and exciting global technology hub".
The companies would not comment on details. There is speculation that Land Securities could reduce the number of long-term advertisers or cut the length of their tenancies.
Introducing more real-time and topical ads could drive up revenue from the site, which observers estimate could bring in more than £20m a year.
Coca-Cola, McDonald’s and Samsung are among those with tenancies. Another screen, The Curve, allows temporary advertisers.
Land Securities previously worked with Clear Channel on The Curve but handled other relationships directly.
