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Rachel Reeves has denied claims of plagiarism, after it emerged passages of her new book were lifted from sources including Wikipedia.
The Financial Times reported the shadow chancellor's book included reproduced material without acknowledgment.
A spokesperson for Ms Reeves rejected the accusations, adding: "These were inadvertent mistakes and will be rectified in future reprints."
Tory chairman Greg Hands said the claims were "potentially very serious".
The book, The Women Who Made Modern Economics, was launched at an Institute for Government event on Wednesday evening.
The Financial Times said its reporters had spotted more than 20 examples of apparent plagiarism, including entire sentences and paragraphs.
It said these mostly contained biographical information.
The BBC has checked the examples highlighted by the FT and found some material in the book was very similar to online sources.
For example, a sentence about the relationship between author H.G. Wells and economist Beatrice Webb is identical to one on Ms Webb's Wikipedia page.
Another paragraph about international aid under New Labour is very similar to a foreword written by Hilary Benn, who is now the shadow Northern Ireland secretary, on the Tony Blair Institute for Global Change website.
Only a few words in the paragraph in the book differ from Mr Benn's foreword.
Publisher Basic Books said: "When factual sentences were taken from primary sources, they should have been rewritten and properly referenced.
"We acknowledge this did not happen in every case. As always in instances such as these, we will review all sources and ensure any omissions are rectified in future reprints."
The statement added: "At no point did Rachel seek to present these facts as original research.
"There is an extensive and selective bibliography of over 200 books, articles and interviews.
"Where facts are taken from multiple sources, no author would be expected to reference each and every one."
Mr Hands said Ms Reeves needed to "explain herself urgently".
"Labour literally have no new plans for this country," he wrote on X, branding Ms Reeves a "copy and paste shadow chancellor".
A source close to Ms Reeves said she wrote the book herself but was helped by research assistants, who worked on biographical material.
They stressed "this is factual stuff, not views, policies or ideas".
Ms Reeves, a former Bank of England economist, is hoping to become the country's first female chancellor if Labour wins the next general election.