The advertising community has traditionally opposed a merger because it believes competition between the two companies' sales houses ensures better value media buying.
"This is nothing seismic. I think ITV is showing greater recognition of our concerns about a TV sales monopoly,
said Malcolm Earnshaw, ISBA's director-general.
Speaking at the ISBA conference last week Morrison urged advertisers to accept a merger, saying only a unified ITV could counter increased competition from a resurgent BBC and a growing BSkyB.
Angus Porter, managing director, BT Retail, said: "Posturing is not helpful. We have to look for a long-term solution. I think a single ITV is becoming increasingly likely, but it's not inevitable."