A former GCHQ specialist says he was recruited by a Republican Party researcher to help verify emails apparently hacked from Hillary Clinton’s private server by Russia.

The claims come amid allegations of collusion between Donald Trump’s presidential campaign and Russian intelligence last summer.

Matt Tait said he was approached around the time WikiLeaks published 20,000 hacked Democratic National Committee emails and Mr Trump publicly called for Russia to obtain Ms Clinton's private server emails.

Democratic Congressman Joaquin Castro called for the House Intelligence Committee to hear from Matt Tait as soon as possible on Saturday.

In a post published on the Lawfare national security blog, Mr Tait describes a series of phone calls with political operative Peter Smith, and later with one of his associates John Szobocsan, from July to mid-September 2016.

Mr Smith, a seasoned opposition researcher claiming to work with the Republican Party, said he was searching for the 33,000 emails Ms Clinton deleted from her private server used for official business while secretary of state.

He asked for Mr Tait’s help in verifying the authenticity of emails obtained via the "dark web". Mr Smith said he wanted to make the emails public before the election in November, and expressed indifference at Russia’s potential role in their release, according to Mr Tait.

The American allegedly discussed “his conviction that Clinton’s private email server had been hacked – in his view almost certainly both by the Russian government and likely by multiple other hackers too – and his desire to ensure that the fruits of those hacks were exposed prior to the election.

"They had a reckless lack of interest in whether the emails came from a Russian cut-out,” Mr Tait says in the blogpost.

Mr Smith appears to have known enough details about the Republican campaign to suggest he was closely tied to them.

In a recruitment document from September 2016, he listed officials including Steve Bannon, Kellyanne Conway and then foreign policy adviser Mike Flynn as being associated with his research company. Mr Bannon has denied meeting with Mr Smith.

Mr Smith died just over a month ago at age 81, just ten days after speaking to the Wall Street Journal about his search for Clinton's emails.

He had a long history of tarnishing opponents of the Republican party and had in the past tried to find a woman to claim Hillary Clinton had an illegitimate child.

Mr Tait, who now runs a UK-based security consultancy, believes he was approached because he had publicly studied Hillary Clinton’s emails as well as the hack of Democratic National Congress emails.

The former information security specialist wrote: "My suspicion then and now was that Hillary Clinton’s email server was likely never breached by Russia, and moreover that if Russia had a copy of Clinton’s emails, they would not waste them in the run-up to an election she was likely to win."

He refused to sign a nondisclosure agreement suggested by Mr Smith towards the end of their contact.