As Home Secretary, Blunkett has been responsible for tightening security against possible violence following the September 11, 2001 attacks on the United States.
Blunkett said he is considering leaving the London-based group on Thursday.
Amnesty said British emergency internment laws introduced in the wake of September 11 were a “perversion of justice.”
“This legislation has created a Guantanamo Bay in our own backyard," said Kate Allen, Amnesty's director for Britain, referring to the US military base in Cuba where alleged al-Qaida and Taliban fighters are being held.
In a hard-hitting report, Amnesty said the emergency legislation adopted by Britain had created a "shadow" criminal justice system for foreigners suspected of being "terrorists".
By allowing foreign nationals to be locked up indefinitely without charge or trial, the government had failed to meet international standards, said Amnesty.
The report said the Anti-terrorism, Crime and Security Act 2001 was discriminatory- “there is one set of rules for British citizens and another for nationals of other countries”.