Christopher Steele, the former MI6 agent who investigated President-elect Donald Trump's alleged links to Russia, "was frustrated" at the inaction of intelligence agencies he handed his dossier to, it has been reported.

Steele, now a director of London-based Orbis Business Intelligence Ltd, was hired both by Republicans and Democrats to dig up dirt on Trump in the run-up to the US election.

But after he decided the information he was receiving was "sufficiently serious", he passed on his findings to the Federal Bureau of Investigations (FBI) and, later, MI6.

After months of uncertainty as to how seriously the FBI was taking his dossier, Steele told American publication Mother Jones about his findings, believing it was of sufficient public interest.

"This was something of huge significance – way above party politics," he said. "I think [Trump's] own party should be aware of this stuff as well."

At the time, the FBI seemed to be more preoccupied with investigating the Democratic nominee Hillary Clinton and her handling of private email servers during her time as the US secretary of state.

As the election approached, FBI Director James Comey publicly released his bombshell letter saying that Clinton would face another investigation.

Steele, 52, reportedly fled his gated home in Surrey after the report was published in full by news website Buzzfeed, hours before his identity was revealed.

The document alleges that Russian intelligence has compromising information that could be used to blackmail the president-elect when he takes office on 20 January. The dossier includes the unverified claims that Trump has close, covert links to high-level Russian officials who assisted his presidential election campaign, and that Trump was filmed watching prostitutes urinate on each other on a bed used by Michelle Obama.

However, Steele's status as a former British spy threatened to cause a diplomatic row, with the Russian embassy in London reportedly suggesting he was still working on behalf of the British government to undermine both Trump and Russia.

Theresa May, in a press conference on Friday (13 January), said the British government had nothing to do with Steele's dossier.

"From everything, you will have seen it is absolutely clear that the individual who produced this dossier has not worked for the UK government for years," she said, reported the Telegraph.

On Friday, the US Senate Intelligence Committee confirmed it will investigate alleged links between Trump and Russia, using "subpoenas if necessary", Politico reported.