LONDON—The U.K. emerged from its longest double-dip recession since World War II, data published Thursday showed, but temporary factors such as the London Olympics may mask deep-rooted problems and economists expect growth to be weak for some time to come.

The U.K. government said preliminary estimates showed gross domestic product grew a stronger-than-expected 1% for the three months ended in September from the second quarter—its biggest rise in five years, and ending a nine-month stretch of contraction....