The revelation that a tip-off from Alexander Downer triggered the FBI probe into Russian meddling in the Trump campaign put the Five Eyes intelligence-sharing arrangement at risk, Joe Hockey has revealed.

The recently departed US ambassador stressed the importance of American intelligence to Canberra, warning the FBI and CIA were under "profound attack" over the former Australian foreign minister's tip-off to US authorities and "it could have gone really badly for us".

Alexander Downer was an unwitting catalyst for the FBI probe. Credit:Photo: Peter Braig

A move to downgrade the information-sharing arrangement would have been a significant blow to Australia, with US intelligence instrumental in stopping nine out of the past 13 foiled terror plots in the country.

The explosive revelations come amid uncertainty over what Britain's decision to allow Huawei into its 5G network means for the Five Eyes intelligence-sharing arrangement.