The result would be a "checkpoint society" where identity checks become an unavoidable part of daily life, Big Brother Watch says.

The group says such a system would fundamentally alter the relationship between citizen and state, creating a surveillance infrastructure vulnerable to abuse, discrimination, and hacking. A Big Brother Watch poll, carried out by YouGov, shows that 63 percent of Brits don't trust the government to protect their data – hardly surprising given Whitehall's track record of bungled IT projects, data leaks, and multi-billion-pound write-offs.

The group has also sounded the alarm over the UK's existing digital identification system, One Login, which underpins the credential issuing process in the so-called "BritCard" proposal, which it says is known to suffer from substantial cybersecurity and data protection weaknesses.

Big Brother Watch also warns of mission creep, arguing that once a system is live, "voluntary" quickly becomes mandatory. Those who fail or refuse to enrol risk being locked out of jobs, housing, or healthcare, while errors could leave people wrongly excluded from essential services.

"The notion that digital ID will provide a magic-bullet solution for unauthorised immigration is ludicrous," said Rebecca Vincent, interim director of Big Brother Watch. "It will not stop small boat crossings, and it will not deter those intent on using non-legal means of entering the country from doing so. But digital ID will create a huge burden for the largely law-abiding 60 million people who already live here and insert the state into many aspects of our everyday lives."