* Michael Bishop, Crispin Davis ruled out for chairman role
* COO Cresswell to leave ITV once new CEO found
* Cresswell to be interim CEO while search goes on
* ITV says searching for chairman with "all due speed"
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LONDON, Oct 12 (Reuters) - ITV Plc said two contenders to succeed Michael Grade as chairman of Britain's biggest free-to-air commercial broadcaster had ruled themselves out, dealing a fresh blow to its long search for new leadership. John Cresswell, ITV's chief operating officer, agreed to take on the role of interim chief executive but planned to leave the company once a permanent incumbent had been found, ITV said on Monday.
ITV, facing the worst advertising downturn for decades, has been searching for a new chief executive since May when Grade, then executive chairman, said he would step back from the day-to-day running of the company.
Its search for a chairman, who will select the next chief executive, began in September when Grade agreed to leave ITV altogether after it failed to secure former BSkyB boss Tony Ball as chief executive.
ITV, which said as recently as Sept. 25 the search for a new chairman was "well advanced", said both former Channel 4 and BMI British Midland chairman Michael Bishop and former Reed Elsevier chief Crispin Davis had ruled themselves out as candidates for the position of chairman.
"The (nominations) committee has revised its shortlist accordingly and is continuing its search with all due speed," ITV said in a statement.
Cresswell, who had been seen as a contender for the post of of chief executive, would leave to "seek a fresh challenge", ITV said.
Simon Fox, chief executive of HMV Group, also previously held talks about the ITV chief executive post but chose to stay at the retailer. (Reporting by Paul Hoskins; Editing by Paul Sandle)