Britain's spy agencies played a crucial role in alerting their counterparts in Washington to contacts between members of Donald Trump's campaign team and Russian intelligence operatives, the Guardian has been told.

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.

Another source suggested the Dutch and the French spy agency, the General Directorate for External Security or DGSE, were contributors.