He also declined to say whether he had talked to Mr Trump about the complaint, saying any such conversations would be covered by executive privilege.

Elsewhere in Mr Maguire’s long-awaited testimony he defended the conduct of the whistleblower, who claimed that Mr Trump was trying to get the Ukrainian president to investigate Joe Biden, the Democrat seeking to challenge the president at the 2020 election.

Mr Maguire said that the whistleblower – whose identity he said he does not know – acted in "in good faith", "by the book" and in line with the law. Those comments amount to a rebuttal of remarks made by Mr Trump.

On Thursday night The New York Times reported that the whistleblower is a male CIA officer who was once detailed to work at the White House, referencing three people familiar with his identity. The report could not be independently verified by this newspaper.

A recording also emerged of Mr Trump saying at a close-door meeting he wanted to find out who gave information to the whistleblower, adding “You know what we used to do in the old days when we were smart with spies and treason, right?”

The president has claimed that the whistleblower was motivate by partisanship and has questioned the person's loyalty to America.

Asked if the whistleblower had shown disloyalty to America or was beholden to another country, Mr Maguire responded: “Sir, absolutely not.”

A new PBS/Marist poll published on Thursday revealed that public sentiment on impeaching Mr Trump appears to have shifted.

The survey, which was conducted on Wednesday, found that 49 per cent of American adults now approved of a formal impeachment inquiry in the House of Representatives, with 46 per cent disapproving and 5 per cent unsure. This compared to a similar poll in May, in the aftermath of a report into the Russia investigation, which found that 53 per cent said they did not want Mr Trump to be impeached.

A redacted version of the whistleblower complaint can be read here: