The British government is, at last, moving to reform the country’s notorious libel law, which has long made London a magnet for frivolous lawsuits. The reform proposal presented to Parliament last week by Kenneth Clarke, the justice secretary, is far from perfect but represents a reasonable first effort to change a law regarded as so unfair that it has been condemned by the United Nations. Last summer, President Obama signed a bill blocking enforcement of British libel judgments in American courts.

Under British libel law, a defendant is guilty until proved innocent. A plaintiff does not have to show damage to his reputation. Further, under the 1849 Duke of Brunswick rule, each individual newspaper sale — or hit on a Web site — counts as a new publication and thus another libel. The law also treats opinion, however measured, just as it treats tabloid gossip until a defendant convinces a court it should be accepted as fair comment.

As a result, London has become, in effect, a center of libel tourism, and the Royal Courts of Justice favored tribunal for what a House of Commons report called “blatantly inappropriate cases, involving foreigners suing foreigners.”

The new American law — the Securing the Protection of our Enduring and Established Constitutional Heritage Act — bars American courts from recognizing defamation judgments by foreign courts if they are inconsistent with First Amendment protections. But it is no way an answer to problems of British libel law itself.

Mr. Clarke introduced the bill with lofty rhetoric. “The right to freedom of speech is a cornerstone of our Constitution,” he said. “It is essential to the health of our democracy that people should be free to debate issues and challenge authority.”

The bill includes a requirement that statements must cause the defendant “substantial harm” in order to be considered defamatory. The bill would allow defendants to claim “responsible publication on matters of public interest” as an argument in their favor. It does away with multiple libels and reduces London’s attractiveness as a lawsuit destination by requiring plaintiffs to prove that England or Wales is “clearly the most appropriate place” to sue someone who doesn’t live in Europe.

The proposed barrier against jurisdiction is significant and a welcome change. In most other respects, the bill is not nearly as protective of speech as American law, and the burden remains on the defendant. Still, the bill has the potential to bury London’s deserved reputation as the world’s libel capital. It deserves the measured praise it is drawing.