Cable & Wireless has suffered a further blow with the departure from its Mercury subsidiary of Maev O'Sullivan, who was director of strategic and commercial development in the telecommuications company.
The news emerges within days of the abrupt resignation of Duncan Lewis, the fourth chief executive of Mercury to leave within the past six years.
Ms O'Sullivan left several weeks ago, but the move was not made public. She was widely regarded in the industry as a leading expert in telecommunications regulation and an invaluable asset to the C&W group.
According to one senior colleague: "She is irreplaceable."
The continuing upheavals at Cable & Wireless have sparked speculation over the future of its chairman, Lord Young, and also caused nervousness in the City.
The company's shares, under pressure since Mr Lewis's departure was announced, yesterday fell another 5p to 413p.
One former employee said yesterday: "The only hope now is break-up. The Cable & Wireless idea of a worldwide federation of companies was fine. But in practice everyone looks to the short-term profit of their own unit and not to the good of the group as a whole."
It was also announced this week that James Ross, group chief executive, is to be deputy chairman in addition to his existing role. At the same time Rod Olsen, finance director, is to take on sweeping new responsibilities in the area of day-to-day management, taking on some of Mr Ross's duties. There is a growing view that Mr Ross is positioning himself as Lord Young's successor with Mr Olsen as second in command.
C&W has refused to comment on Mr Lewis's departure after only nine months in the job, other than to cite "personal reasons". His departure shocked the industry as he was seen as highly ambitious and as having, in effect, begun to turn Mercury around.
There has been speculation that Mr Lewis left because he was told to go, or to accept a seat on the group's main board - in spite of his reported opposition to some of C&W's strategies and policies.
But one industry source said: "Duncan left because the only seat he wanted was that occupied by James Ross and he could not have it."
Separately, John Carrington, until now C&W's director for the Caribbean, the Middle East and Africa, is to take up the post of managing director of Mobile Systems International, a six-year-old company founded by Mo Ibrahim.
Mr Carrington was the founding managing director of Cellnet and of Mercury One2One, C&W's mobile joint venture with US West.