His departure immediately led to speculation he would join Cable & Wireless Communications, the new cable television and telephony group which includes Mercury, Mr Lewis's former company. C&W is actively seeking a chief executive for the group.
Neither Mr Lewis nor Granada, the hotels-to-television conglomerate, would comment in detail on his departure. In a curt statement, Granada said: "Both Duncan and Granada Group management have recognised an incompatibility of approaches and have therefore agreed to part on an amicable basis."
It is understood that Mr Lewis felt the main group management, headed by Mr Robinson and Mr Allen, were not committed enough to the media side of the business, and there had been disagreements about acquisition strategy.
Mr Lewis left the Granada headquarters on Wednesday, following a meeting with Mr Allen. He has not returned since. He had been on a rolling one- year contract of pounds 250,000 a year, which is expected to be bought out.
A spokesman for Granada said that Mr Lewis's appointment had been "a brave experiment" that had gone wrong. Added a company insider: "He didn't know anything about television, and it showed."
Granada Media Group denied there had been any basic disagreement over strategy. "In a company such as this, there has to be good relations between the group and the chief executives of the divisions," the spokesman said. "For some time, it was clear things were not going well."
It is understood that Granada's senior executives were also concerned about Mr Lewis's management style, which some have styled too "showy". As well, he is believed to have spent as much as pounds 500,000 on developing strategy papers for the media group, an amount that was viewed at head office as excessive.
There were suggestions last night that Mr Lewis had wanted to invest aggressively, and had looked at joint venture production in the US, City- TV stations in Britain and other operations on the Continent. To date, most of Granada's television investments have been confined to the ITV sector.
Some of his past colleagues have said Mr Lewis was "mercurial" and lacked focus. At Granada, his short tenure was marked by several rows with Mr Robinson and Mr Allen, who used to run the television business before rising to chief executive.
Mr Allen, the dour Scot who acts as the details man to Mr Robinson, the flamboyant strategist, was understood to have been particularly uncomfortable with Mr Lewis. Granada declined to comment on suggestions that the two had a furious row on the day Mr Lewis left the building.
Mr Lewis, 45, moved from BT to Cable & Wireless, where he rose to become chief executive of Mercury, a job he held for only nine months. His departure was said to have followed disagreements with management.
He had been a surprise choice for the job at Granada, where he oversaw the company's television interests. Granada owns the Granada and London Weekend Television franchises, 27 per cent of Yorkshire-Tyne Tees, and 60 per cent of Granada Sky Broadcasting, a joint satellite television venture with Rupert Murdoch's BSkyB.
Mr Lewis's replacement is Steve Morrison, a long-serving Granada executive, who became managing director of Granada Media Group earlier this year when the operations were restructured.
Granada has been preoccupied in recent months by the need to sell unwanted hotel assets it inherited following the bitter takeover early this year of Forte, the hotels and restaurant group.
But the Granada spokesman denied the company had been neglecting its extensive media operations, pointing to its investments in ITV and its growing production businesses in the UK and overseas.