Theresa May has been accused by senior peers of misquoting a parliamentary committee to justify granting the Government "unprecedented and extraordinary" powers in the Brexit repeal Bill.
The House of Lords Constitution Committee said the legislation, formally known as the European Union (Withdrawal) Bill, "weaves a tapestry of delegated powers that are breath-taking in terms of both their scope and potency".
Committee chairwoman Baroness Taylor of Bolton accused ministers of misquoting and ignoring a previous report by the senior peers, which called for tougher parliamentary oversight of so-called "delegated powers".
It comes after Mrs May used Prime Minister's Questions on Wednesday to brush off accusations from Tory Remainer Anna Soubry that the Bill amounted to an "unprecedented and unnecessary Government power grab".
The PM insisted the so-called Henry VIII powers to make changes to EU laws as they are repatriated using secondary legislation, and without full parliamentary scrutiny, were required to "make corrections" so Britain can leave the EU in an orderly manner.
She also claimed the approach had been "endorsed by the House of Lords Constitution Committee", apparently referring to a report from earlier this year.
But releasing a new interim committee report on the Bill, Lady Taylor said: "The EU (Withdrawal) Bill represents an extraordinary transfer of legal powers from Parliament to the Government, without the additional oversight we recommended. We believe this will create very real difficulties for Parliament in fulfilling its constitutional role to scrutinise this Bill.
"We acknowledge that the Government needs significant powers in order to deliver legal certainty after Brexit. However, we warned the Government that such powers must come with tougher parliamentary scrutiny mechanisms and we are disappointed that we have not only been misquoted by the Government, but that our key recommendations have been ignored.
"The committee will launch a full inquiry on the EU (Withdrawal) Bill shortly."
The issue has emerged as a major battleground on the Bill, which Labour has said it will oppose because it represents a "power grab", and which will be debated by MPs for the first time at second reading on Thursday.
Ms Soubry and other senior Tories have also raised concerns about the powers granted to ministers by the legislation, raising the prospect of Mrs May's minority Government being defeated in House of Commons votes in the Bill's later stages.
In the interim report, the peers warned the Bill raises "fundamental constitutional questions about the separation of powers between Parliament and Government".
It also drew attention to "multiple uncertainties and ambiguities" and called on the Government to ensure the legislation gives certainty to individuals, organisations and the Government so they know exactly what the law is post-Brexit, without having to resort to litigation.