Hillary Clinton said the Brexit vote was blighted by "fabricated and false" information from the leave side similar to the fake news campaigns that blew up around the US presidential election.
The former Democrat presidential contender said the EU vote was a "precursor to some extent" of the American election in that both were affected by an "explosive spread" of untrue stories.
"The amount of fabricated, false information that your voters were given by the Leave campaign," she told the Andrew Marr show.
"I'm very familiar with what the leave side said because they transported a lot of that on behalf of Trump."
She warned that democracies have "some thinking to do" about how to ensure that truth wins out.
"There has to be some basic level of fact and evidence in our politics."
Mrs Clinton also warned that a no deal exit from the EU would be "a very big disadvantage to Britain" and could drive business to move jobs abroad.
"I think the disruption for Britain could be quite serious," she said.
She warned against those who argue Britain could depend on bilateral deals with partners including the US.
"You're making a trade deal with someone who doesn't believe in trade," she said of President Trump.
She also addressed her election, admitting that she had fully expected to win against Mr Trump.
Mrs Clinton has ruled out running for the US Presidency again but says she hopes to see another woman take the top job.