India's Supreme Court ruled on Thursday that citizens have a constitutional right to privacy, a landmark verdict that could have wide-reaching implications for the government's flagship biometric programme.

Privacy is not explicitly mentioned in the Indian constitution, and the government has argued that India's 1.25 billion citizens cannot expect an absolute right to privacy.

But in a brief statement on Thursday, Chief Justice J.S. Khehar said privacy was “protected as an intrinsic part of Article 21 that protects life and liberty”.

The Supreme Court set up a special bench to rule on the issue after petitioners challenged the government's Aadhaar biometric programme, which has recorded the fingerprints and iris scans of more than one billion Indians.

Aadhaar was set up as a voluntary scheme to streamline benefit payments to millions of poor people and cut fraud.

But in recent years it has become compulsory for a growing number of services, including opening a bank account or paying taxes.

Opponents say that its use for what are effectively essential services means their right to privacy is increasingly being violated.

Lawyer Prashant Bhushan said after the judgement it would likely impact the Aadhaar programme.

“Any fundamental right is subject to reasonable restrictions by law. Whether the Aadhar Act imposes unreasonable restrictions will have to be examined,” he told reporters outside the court.

Prime Minister Narendra Modi's government has rejected suggestions that the programme, set up in 2009, poses a threat to civil liberties, despite personal data being leaked in security breaches.

In May, attorney general Mukul Rohatgi rejected suggestions that Indians could refuse to provide their iris scans or fingerprints to the government, telling a court “the concept of absolute right over one's body was a myth”.

During the hearings the nine-member Supreme Court bench recognised the risk of personal information being misused, and the challenge of protecting such private data in the internet era.

But the judges also acknowledged there must be restrictions within reason on individual privacy.

Constitutional law scholars had said the case would be a litmus test of Indian democracy, with potentially far-reaching consequences if individuals were allowed to challenge laws on the basis of individual rights.