Broadcasters Granada and Carlton Communications will join up to try to increase their advertising revenues and number of viewers, a Carlton spokesman has said.
The collaboration over programme scheduling and marketing follows aborted merger talks earlier this year.
But regulators fear a full merger could give the combined group too much power over the price charged to advertisers.
Granada and Carlton, the biggest ITV franchise holders, have been suffering from the advertising recession and the collapse of their joint pay TV venture, ITV Digital. Recent industry figures show ITV is losing viewers and advertising revenue to the competition.
Carlton chief executive Mr Gerry Murphy described the collaboration to the Financial Timesas creating a "virtual enterprise", without actually combining the advertising sales forces of the two companies.