George's departure was widely anticipated in the industry following the appointment of ex-Virgin chief executive Fru Hazlitt as managing director of GCap London in January.
George's announcement, revealed on Mediaweek.co.uk, came the day before GCap's full-year figures were due to be released.
He told Media Week: "I played a key role in the restructuring of the company after the merger (between Capital Radio and GWR).
"I wanted to see through the creation of a strong operation and I believe I have done that."
Reports anticipating the results predicted a "meltdown" and "some of the worst (results) since GCap was forged", as well as speculating about cost-cutting and the sale of more stations.
But sales director Daglish strongly denied the speculation, telling Media Week there were "no plans to sell anything off".
He said: "We are doing incredibly well and the results reflect last year, which is nowhere near where we are currently. There are no shock announcements to come."
Daglish denied speculation that Nick Hewat, Virgin Radio's sales director, would be joining GCap and said Hazlitt and George had a good working relationship.
The pair first worked together when Hazlitt was named head of client sales at Capital Radio Sales in 1995 and reported to George, then sales director.
Two years later, she was promoted above George to the role of sales director at new sales house Capital Sales and Marketing.
George then left to set up GWR's sales operation Opus and became commercial director when GWR and Capital Radio merged in 2005.
Hazlitt had by then moved on to the top job at Virgin Radio, from which she resigned in January.
Other options for GCap include reversing the controversial decision to cut the number of ads played on Capital 95.8.
Hazlitt herself was an early critic of the two-in-a-row format, which has lost the company millions of pounds in revenue, though chief executive Ralph Bernard is said to be standing firm.