US whistleblower's letter claims White House cover up

Let's begin in the US where a whistleblower complaint against the US president has accused Senior White House officials of a cover up. The whistleblower's letter was released a few hours ago and it contains several explosive claims, including that the White House sought to hide the transcript of President Trump's phone call with the Ukraine leader - in a top-secret computer protected by a covert code-word. In a committee hearing that ended shortly before we came to air - Acting Director of National Intelligence Joseph Maguire testified to the House Intelligence Committee, and is now due to face a closed-doors session with the Senate Intelligence Committee. Joining us now from Washington is our correspondent Simon Marks with the latest update.