A spokeswoman for M&S said: "We can confirm that an individual has been dismissed. It was a long-thought-out process, but the individual deliberately leaked information to the media, which was derogatory and speculative. He did not use internal channels, and might have done it again."
The spokeswoman added that other employees had written letters of support for the way the company dealt with the matter.
Maria Ludkin, legal officer at trade union GMB, which represented the staff member, said: "M&S has shown that it is more concerned about maintaining a repressive regime for staff than promoting open discussion about the direction of the company and the way staff are treated."
GMB said it intends to "secure justice" for the employee.
M&S whistleblower sacked
Marks & Spencer has sacked an employee for telling a national newspaper about redundancy cuts that came into effect this month.
