Sources say Warner, who is planning to set up her own company, is in talks with senior executives at the channel to try and secure a 'sweetheart' deal. She is expected to leave at the end of August after her duty as commissioning editor of Big Brother 2 ends.
It is unclear whether she will be replaced or whether the Ideas Lab, set up in 1999 will continue and insiders have bitterly criticised its low yield and lack of vision.
This year Warner ordered Jailbait, a 50-minute piece looking at teenagers in relationships with older men, from Maverick Television. She was also involved with Celebrity Big Brother.
Meanwhile, Channel 4 head of documentaries Peter Dale has ended his six-month search for a commissioning editor with the appointment of E4 commissioning editor, factual, Danny Cohens.
Cohen, who moves across in September, has been briefed to deliver six to 12 popular, one-off documentaries per year to air between 21.00 and 23.00 as well as to nurture late schedule series.
He will join Dale and Hilary Bell (Cutting Edge) in the documentaries department, filling the space left by Ros Franey, who left to become a freelance producer last December.
In addition, C4 deputy commissioning editor, independent film and video, Jess Search has moved over to look after experimental late-night strand 4 Later.