LABOUR will withdraw support for new surveillance powers if no safeguards are provided to prevent spying on trade unionists, shadow home secretary Andy Burnham said yesterday.

He said it would be an “abdication of responsibility” for public safety to adopt outright opposition to the government’s Investigatory Powers Bill at its second reading and ordered Labour MPs to abstain in the vote.

But Mr Burnham warned Home Secretary Theresa May that Labour would sabotage the Bill’s progress through Parliament unless she offered more privacy protections.

He recalled how campaigners had been subjected to “inappropriate police investigation” in some of the “darkest chapters” of Britain’s history.

Specifically, he raised the case of the Shrewsbury pickets — 24 workers charged with various offences after taking part in the 1972 builders’ strike over safety.

Declassified government files reveal how their prosecution was “politically orchestrated with the help of the police and security services,” the shadow home secretary said.

And he told his Tory counterpart: “We need to go further in giving the full truth about some of the darkest chapters in our country’s past so that we can learn from them and then build the right safeguards into this legislation.”

Ms May has already bowed to calls for a “double lock” on surveillance powers, requiring spooks to receive both judicial and political authorisation.

She claimed privacy is now “hard wired” into the Bill, which “imposes high thresholds on the use of the most intrusive powers.”

But unions have raised concerns that that the legislation still grants spies access on the basis of “economic well-being” as well as “national security” grounds.

Mr Burnham insisted that clause must be removed to “build confidence that there can be no targeting of law-abiding trade unionists, as we have seen in the past.

“This Bill will have failed unless it entirely rules out the possibility that abuses of the kind I have mentioned can ever happen again.

“That is a clear test I’m setting for this Bill.”

Labour MP Steve Rotherham added: “It’s absolutely essential that there’s the strongest possible safeguard in the Bill that would specifically make sure that such great historic injustices can never happen again.”

Tory MPs such as David Davis and Edward Leigh also called for privacy rights to be beefed up.