HONG KONG — The Hong Kong democracy activist Nathan Law said on Monday that he had applied for political asylum in Britain, a petition that will likely inflame tensions with China if granted.

Mr. Law, 27, fled to London in June, just before a new national security law gave Hong Kong sweeping powers to quash dissent after months of fiery anti-government protests.

Mr. Law rose to prominence in Hong Kong as a student leader in 2014, calling for freer elections in the semiautonomous Chinese territory through street demonstrations and sit-ins. Two years later, at age 23, he became the city’s youngest elected lawmaker, though he was disqualified the following year over altering his oath for office.

Mr. Law was jailed in 2017 on charges of inciting the street protests three years earlier. His close ally, Joshua Wong, was sentenced to more than a year in prison this month over a protest in 2019 and faces additional charges over his activism.