The chairman of the House Intelligence Committee investigating alleged ties between Donald Trump’s campaign and Russia has reportedly exhibited odd behaviour, participating in a “peculiar midnight run” to see secret documents and not being transparent with his colleagues.

Devin Nunes, a former Trump adviser, reportedly jumped out of an Uber ride on Tuesday night to see potentially critical documents relating to the investigation of Trump aides, without informing his fellow passenger, a senior Washington staffer on the committee.

His committee’s investigation has since stalled following a series of unusual events.

This comes shortly after a hearing where FBI director James Comey confirmed he was investigating possible collusion between Russian operatives and Trump aides, and the Committee’s senior Democrat Adam Schiff said he and Mr Nunes subsequently had a classified briefing which gave him “more than circumstantial” evidence of such collusion.

Mr Nunes has not shared the documents he obtained during his “peculiar midnight run” this week with his Democratic colleagues in the committee, said Mr Schiff.

He instead called an impromptu press conference to announce that he had seen dozens of intelligence reports which showed that Mr Trump’s aides were subject to “incidental data collection”, that is caught in a foreign surveillance net cast by US spy agencies.

California Democrat Schiff and Mr Nunes put in a joint request to Mr Comey to share with their committee the information given to them in the classified briefing. But before an answer could be given, Mr Nunes cancelled a second scheduled hearing for 28 March, where intelligence chiefs were expected to speak.

Mr Nunes said he called off the meeting to have more time to confer with Mr Comey and the National Security Agency director Michael Rogers.

He did not say what exactly what was in the documents or who had shown them to him.

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Instead, he briefed the President, who recently claimed he had been illegally wiretapped by his predecessor in collusion with the UK.

“I had a duty and obligation to tell him because, as you know, he’s taking a lot of heat in the news media,” said Mr Nunes, who served on the Trump transition team.

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Mr Nunes’ behaviour and the cancelling of the hearing have raised questions over the credibility of the committee’s investigation.

“The chairman has to make a decision over whether he is a surrogate for the President, as he was during the campaign and transition, or whether he’s leading a bipartisan investigation, because he can’t do both,” Mr Schiff told the San Francisco Chronicle.

“This week, unfortunately, he behaved like a surrogate and that is a real problem.”

Mr Schiff said he was determined to “soldier on” with the committee, however, otherwise the investigation could completely collapse.