Burnham exchanged messages with a person posing as a White House contact in what has been described as a security breach.
The available information states that the exchange involved Burnham and a White House imposter, but no further details have been provided about the timing of the messages, their contents, how the impersonation occurred or how it was discovered.
Downing Street has declined to comment on the breach. The material supplied does not include any statement from Burnham or any official explanation of whether sensitive information was shared.
The incident was first reported by Politico. The latest known position is that Downing Street has not issued a comment, and further details about the breach remain unavailable.
