A man who is challenging the government's bid to annul some 20,000 Covid vaccine exemption certificates has been granted legal aid for the case.

Kwok Cheuk-kin's application for legal aid had earlier been rejected on the grounds that he's not directly affected by the case because he's triple-jabbed.

But speaking outside the High Court on Tuesday, Kwok said he has successfully appealed against the decision.

"The reason for the successful appeal is that it's a case of public interest and the Legal Aid Department should not reject me," Kwok cited the judge as saying.

Kwok, who is also dubbed "king of judicial reviews" for the numerous legal challenges he filed, will return to court on Thursday for a hearing on his judicial review on the government's attempt to invalidate vaccine exemption certificates issued by seven doctors suspected of giving them out without conducting proper medical consultations.

The certificates allow people who are not fully vaccinated to enter premises like restaurants. Government lawyers argue that the invalidation is justified on public health grounds and say that people affected can visit another doctor, including public doctors for free, to seek a new exemption certificate.