GCHQ first became aware in late 2015 of suspicious “interactions” between figures connected to Trump and known or suspected Russian agents, a source close to UK intelligence said. This intelligence was passed to the US as part of a routine exchange of information, they added.

Over the next six months, until summer 2016, a number of western agencies shared further information on contacts between Trump’s inner circle and Russians, sources said.

The European countries that passed on electronic intelligence – known as sigint – included Germany, Estonia and Poland. Australia, a member of the “Five Eyes” spying alliance that also includes the US, UK, Canada and New Zealand, also relayed material, one source said…

It is understood that GCHQ was at no point carrying out a targeted operation against Trump or his team or proactively seeking information. The alleged conversations were picked up by chance as part of routine surveillance of Russian intelligence assets. Over several months, different agencies targeting the same people began to see a pattern of connections that were flagged to intelligence officials in the US.