The prospect of a Lords rebellion against the government's emergency surveillance law grew today, after an influential committee of peers raised concerns about the legislation.
The Lords constitution committee warned the fast-tracking of the bill "is a matter of concern" and said the contents of the legislation gives broad powers to the home secretary.
Clause 1(3) of the bill might allow Theresa May to further expand her surveillance powers without the need for further votes in the Commons.
It is not clear what would "prevent the secretary of state using clause 1(3) to enhance data retention powers", peers said.
The committee also raised concerns about why clauses related to the Regulation of Investigatory Powers Act (Ripa) were found in the bill, given no argument had been made that these needed to be passed under emergency legislation.
The report's findings substantiate the arguments of privacy campaigners and increases the chances that peers might send the legislation back when they debate it later today.
Such a move could extend the parliamentary session and would indicate the government has more of a fight on its hands than it had anticipated.
The data retention and investigatory powers bill (Drip) went through all its changes in a matter of hours last night, with a rump of 33 MPs voting against it at third reading, and 416 voting it through.
A cross-party bid led by Labour MP Tom Watson which attempted to put an end of the year expiration date on the bill was defeated by 454 to 56.
The government did concede two additional reviews: a general review at ministerial discretion by the time of the election and the twice-yearly reviews proposed by Labour.
Ministers said the bill is merely a continuation of the security agencies' existing powers and that emergency legislation was required to stop telecommunications firms destroying files about user behaviour to comply with a European court ruling last April.
Opponents say the bill radically expands the scope of British surveillance laws, and essentially acts as a snoopers-charter-lite. They say the government has had since the April judgement to come up with a legal response but that a theatrical emergency has been constructed to escape parliamentary scrutiny.
"It is outrageous that we have been granted one day in which to debate and scrutinise a bill of such significance," Green MP Caroline Lucas said.
"It is even more outrageous that this is being blamed on a totally manufactured emergency and represented as doing nothing other than maintaining the status quo.
"That is not accurate. This is a huge power grab under false pretences."
Former Labour shadow minster Diane Abbott said her party's leadership had been hoodwinked into supporting the legislation.
"I believe - I hate to say this because they are all nice people - that those on the opposition front bench have been rolled," she said.
"All ministers had to do was to raise in front of them the spectre of being an irresponsible opposition, and that children will die if they do not vote for the bill on this timetable, and they succumbed."
Theresa May warned: "If we delay we face the appalling prospect police operations will go dark, that trails will go cold, that terrorist plots will go undetected.
"If that happens, innocent lives may be lost."
Shadow home secretary Yvette Cooper replied: "The home secretary will recognise that parliament has been put in a difficult position by this emergency legislation this week.
"This is not the way that this kind of legislation should be done. Let's be clear, the last-minute nature of it does undermine trust in the government's intentions but also in the vital work the police and agencies need to do.
"But I also have no doubt this legislation is needed and that we cannot delay it until the autumn."
Meanwhile, the Open Rights Group warned that the government has left itself open to legal challenge.
It suggested the proposed bill ignores the European court ruling that blanket data retention breaches fundamental rights to respect for private life and the protection of personal data.
Drip was constructed so that the UK's data retention laws were not reliant on the EU directive which was made illegal by the court ruling. But the Open Rights Group reminded ministers that national legislation also needed to comply with rulings from the court.
"The government has ignored the CJEU's [court of justice at the European Union] ruling and denied the public a proper parliamentary debate about a law that will violate our human rights," executive director Jim Killock said.
"If they don't end blanket data retention, they are breaking human rights law."