It was previously thought that the pair would work their notice period when they resigned from the agency they founded in late February.
However, it was subsequently agreed they should leave the agency in the interim period. They are likely to be prevented from embarking on competing endeavours until early 2014.
A source suggested that any hopes Miles and Morrison had of spinning off parts of the business were unlikely to come to fruition, as their gardening leave reflected difficulties that had emerged in their relationship with owner King Worldwide.
Five senior executives who left M:Communications in the same week are understood to be on semi-gardening leave for six months, whereby they continue to handle client work away from the office.
Meanwhile, PRWeek understands there have been further resignations within the agency's London team, including recently installed head of technology Juliet Clarke.
Clarke joined to establish a tech arm in October last year from Torex Retail Holdings. It is thought the departure of a handful of more junior staffers have also been announced internally.
An M:Communications spokesperson declined to comment, while Morrison and Miles could not be reached for comment.
Miles and Morrison established M: in September 2002 after being placed on gardening leave from Financial Dynamics (now FTI Consulting) in January of that year and completing a six-month non-compete period.