The whistleblower at the heart of the Trump-Ukraine scandal was facing an uphill battle to keep their identity hidden on Friday amid fierce attacks from the US president and biographic details emerging in the media.

Intelligence figures, Democrats and the whistleblower’s own lawyers insisted it is right that the person's anonymity is protected after their detailed complaint lodged about Donald Trump's behaviour was made public on Thursday.

But Republicans from the White House down have repeatedly called into question the whistleblower’s motives as they attempted to unpick the allegations that have triggered impeachment proceedings.

Mr Trump asked whether the person was a “partisan operative” on Friday, tweeting: “Sounding more and more like the so-called whistleblower isn’t a whistleblower at all.”

There are signs that the American public support the launch of an impeachment inquiry, with three polls taken after the announcement showing more people approving than disapproving and a fourth showing a tie. Before this week polls consistently showed the country opposed to impeachment.

With the full political impact of the whistleblower’s claims beginning to become clear, details of the unnamed individual at the centre of the scandal have emerged in US media reports.