The principle of the law is rooted in the belief that certain crimes — such as genocide, hostage-taking and torture — are so serious that they must be addressed wherever a suspect can be detained.
The amendment, passed by the Queen on Thursday, has made it more difficult for citizens to bring charges against suspects.
The law had been subject to fierce criticism, especially by Israeli officials, after its application led to strained relations between Britain and Israel.
Last year deputy prime minister Dan Meridor and former foreign minister Tzipi Livini cancelled trips to Britain fearing arrest.
But the move to amend the law has been severely criticised by human rights activists and others.
"This marks a backward, nervous step by the U.K., which is reluctant to bring tyrants and torturers to justice if it suits the government to sell them arms or to turn a blind eye to their human rights violations,"
said Geoffrey Robertson to AP, who as a U.N. appeals judge delivered key decisions on war crimes.
"The change in the law has nothing to do — as the U.K. claims — with insuring that cases proceed on solid evidence. No district court judge would issue an arrest warrant lightly."