Marks and sparks' express check-out. (Departures).

LUC VANDEVELDE, 51, chairman and CEO of Marks & Spencer, the venerable London-based retailer, recently relinquished his CEO title after a little more than two years on the job. He was succeeded by Roger Holmes, 42, the former managing director of its U.K. retail unit.

Marks & Spencer says the move was expected; Vandevelde successfully spearheaded a restructuring plan meant to revive the then-faltering company, with adjusted share earnings up 45.5 percent for the year ended March 30. But it also means he has joined an ever-growing club: British CEOs with tenures even shorter than those in the United States and considerably briefer than in some other European countries.

In fact, according to a recent study of 481 companies in 25 countries conducted by DBM, an outplacement firm in Stamford, Conn., the median tenure for British CEOs is two to three years, compared with three in the U.S. What's more, the study found significant differences between CEO turnover in the U.K. versus its historical rival, France, where the median tenure is four to five years.

How come? One possibility is differences in employment legislation. Laws in France provide greater protection to employees than in either the U.S. or the U.K., an approach that may directly affect job security, even at the top. And, since the U.K. tends to be the first country to be influenced by trends in the U.S., it's not surprising that it would be more susceptible to U.S.-style trends in shorter CEO tenure than France. Says Frank Schroeder, president of DBM Europe, "Expectations in [London] very much mirror those on Wall Street."