NSA whistleblower Edward Snowden has voiced his opposition to the Investigatory Powers Bill, which was unveiled Wednesday by the British government, saying ministers are “taking notes on how to defend the indefensible.”

His remarks come as Home Secretary Theresa May has admitted that UK spy agencies MI5, MI6 and GCHQ secretly collected communications data for decades to protect “national security.”

Snowden, who sought asylum in Russia after leaking top-secret documents about American and British mass surveillance techniques, posted a series of tweets condemning the new bill.

He said the powers given to security agencies in the bill amounted to access to “the activity log of your life.”

May announced on Wednesday that internet companies would be required to store a record of every website accessed by users for a year. The new bill also targets encrypted messaging services, such as WhatsApp and iMessenger, which allow users to evade hackers and data collection.

It's not about something to hide, it's about something to lose. — Edward Snowden (@Snowden) November 4, 2015

Snowden expressed his opposition to the bill, which was created in the wake of his revelations.

One Snowden tweet highlights the ease with which British security agencies can get mass warrants to intercept communication data or logs of internet activity.

By my read, #SnoopersCharter legitimizes mass surveillance. It is the most intrusive and least accountable surveillance regime in the West. — Edward Snowden (@Snowden) November 4, 2015

#SnoopersCharter does not require individualized judicial authorization in advance of *interception*. Such a dragnet is mass surveillance. — Edward Snowden (@Snowden) November 4, 2015

“#SnoopersCharter’s ‘judicial oversight’ seems notional, not serious. Judges need power to weigh evidence, propriety,” he said.

He added that collecting web records is like making a “list of every book you’ve ever opened.”

Your web records are not like "an itemised phone bill," they're like a list of every book you've ever opened. #SnoopersCharter — Edward Snowden (@Snowden) November 4, 2015

His comments come after May admitted that huge amounts of data, including texts, emails and phone calls, had been collected secretly by intelligence services for years before the new legislation was introduced.

The government had previously only admitted to collecting data against suspects based overseas, but May revealed that the acquisition of data had taken place in the UK under “national security directions” that formed part of the 1984 Telecommunications Act.

The powers allowed any secretary of state to order a company to “do, or not to do, a particular thing,” May said.

She claimed that the powers had been used to stop a terrorist attack on the London Stock Exchange in 2010.

Bulk data collection began after the 9/11 attacks in 2001, but were greatly increased after the 7/7 London bombings in 2005, the Times reported.

The security services insisted at the time that data collection merely allowed them to “join the dots” between terror suspects during investigations.