British intelligence and security agency GCHQ was the first to intercept messages and establish a link between Russia and US President Donald Trump's aides way back in 2015.

The UK intelligence agency, well known for its advanced cyberspying methods, is said to have become aware of suspicious "interactions" between figures connected to Trump and known or suspected Russian agents in 2015, according to a report in the Guardian. The information was then passed on to US as part of a routine exchange of information.

A number of foreign spy agencies also reportedly passed on similar information to the Central Intelligence Agency. The countries that sent electronic intelligence to US included Germany, Estonia, Poland, France, the Netherlands and even Australia.

The messages were picked up merely through a routine surveillance of Russian intelligence assets, and were not part of any targeted campaign towards Trump as the President had claimed sometime back. Different foreign agencies targeting these same agents began noticing a pattern of connections that were raised to the CIA.

Both the FBI and the CIA were reportedly slow to appreciate the seriousness of these links ahead of the US election. The reason behind the lukewarm response was that the US law prohibits its agencies from examining private communications of American citizens without warrants.

"It looks like the US agencies were asleep," a source was quoted saying about the CIA and other intelligence officers. "They European agencies were saying: 'There are contacts going on between people close to Mr Trump and people we believe are Russian intelligence agents. You should be wary of this.' The message was - Watch out. There's something not right here." said the source.

How did Trump know?

GCHQ's former head Robert Hannigan, has reportedly passed concrete evidence establishing links between Trump aides and Russia to CIA chief John Brennan in the summer of 2016. Brennan used this GCHQ proof and intelligence from other partners to begin an inter-agency investigation. He, in late August and September, gave a series of classified briefings to the Gang of Eight, the top-ranking Democratic and Republican leaders in the House and Senate.

Although Brennan did not reveal the source of his findings, he did say that America's intelligence allies had provided information. It was at this time Trump and his aides reportedly learned of GCHQ's involvement.

Subsequently, Trump and some members of his administration, most notably Sean Spicer, accused former US President Barack Obama of asking GCHQ's help to wire tap the current President. These accusations were rubbished by the British government particularly the GCHQ who called it "utterly ridiculous".