Joe Biden has been accused of plagiarism after it was revealed that he copied passages of his climate policy from other sources.

The $5 trillion (£4 trillion) policy appeared to include passages from documents originally published by the BlueGreen Alliance, a collective of workers’ unions, and the Carbon Capture Collective, a coalition of business and environmental groups.

The groups’ documents were not cited in the policy. The Daily Caller, a conservative outlet, first reported the discrepancy.

“Several citations, some from sources cited in other parts of the plan, were inadvertently left out of the final version of the 22-page document,” a Biden campaign spokesperson said.

The Delaware politician unveiled the ambitious plan on Tuesday, the same day his rival Elizabeth Warren published her climate-change proposals.

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Mr Biden, who is the frontrunner in the Democratic primary race, pledged to lead the US to having net-zero carbon emissions and 100 per cent clean energy by 2050.

The former senator’s failed 1988 campaign for the Democratic presidential nomination was marred by similar plagiarism allegations.

The politician was accused of lifting sections of his campaign speech from a speech by Neil Kinnock, who was then Labour leader.

Mr Biden also admitted to plagiarising for a law school assignment while studying at Syracuse University.

At the time Mr Biden said his student plagiarism was caused by him not knowing how to properly document sources. The scandal helped to end his fledgling campaign.

“Four decades in public life and there’s always one constant,” a Trump campaign spokesperson said.

“What would a Joe Biden candidacy be without a little plagiarism?”

The president also chimed in while in London for his UK state visit.

“Plagiarism charge against Sleepy Joe Biden on his ridiculous Climate Change Plan is a big problem, but the Corrupt Media will save him,” Mr Trump, who has frequently dismissed climate science, wrote.

But others warned that a plagiarism scandal could have little impact on Mr Biden’s popularity in the primary campaign.

The candidate continues to lead in polls, despite having already faced accusations of inappropriate conduct around women.

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“There are many, many molehills that look like mountains during a campaign,” David Axelrod, a Democratic strategist said.

“The challenge for the campaigns and the press is to decide which is which.”