Voters go to the polls in Britain on Thursday in a dyspeptic mood, many of them frustrated with the Conservative government but skeptical that any replacement can unravel the tangle of problems hobbling the country.

Their skepticism is warranted, according to analysts. Even if the Labour Party wins a robust majority in Parliament, as polls suggest, it will confront a raft of challenges, from a torpid economy to a corroded National Health Service, without having many tools to fix them.

The Labour leader, Keir Starmer, would inherit a “legacy of ashes,” said Robert Ford, a professor of political science at the University of Manchester. And voters, who less than five years ago elected the Conservatives in a landslide, are not likely to give Mr. Starmer much slack to turn things around.

“The message could not be clearer: You must deliver change — or you are toast,” Mr. Ford said. “People will not be patient.”

The election is shaping up as a political watershed for the country. It is likely to represent the repudiation of the Conservative Party after 14 years in power, and the elevation of the Labour Party, which less than five years ago suffered its own electoral defeat, the worst since 1935, at the hands of the Conservatives.