Classified information has to be “communicated across appropriate secure systems”, Downing Street has said after it was revealed top US officials had texted plans for strikes against Houthi rebels to a group chat that had accidentally included a journalist.
Senior American government officials, including the defence secretary and national security adviser, messaged plans for an attack on Yemen using the messaging app Signal, it was reported on Monday night.
On Tuesday, Number 10 insisted that it was confident that any UK intelligence shared with the US was being handled appropriately, despite the revelations.
But, when asked if external messaging apps were considered an appropriate place for UK officials to discuss classified information, the Prime Minister's official spokesman said: “No, for any classified information that has to be communicated across appropriate secure systems.”
The US carried out a series of air strikes against the rebel Houthi militant group in Yemen on March 15 following continued attacks on shipping in the Red Sea.
But two hours beforehand, details of the attack had been sent to a Signal group chat that included the US vice-president JD Vance, defence secretary Pete Hegseth and secretary of state Marco Rubio, among others.
Signal chats are encrypted, but are not approved by the US government for discussion of classified material.
The use of the app to provide details of the airstrikes came to light because one participant had accidentally added the editor-in-chief of The Atlantic magazine, Jeffrey Goldberg, to the group.
The US defense secretary blasted European “free-loading” after Mr Vance moaned about “bailing out Europe again”, the leaked messages reveal.
However, the Prime Minister’s spokesman added that the UK is still confident in sharing intelligence with the US.
"The US is our closest ally when it comes to matters of defence, we have a long-standing relationship on intelligence and defence cooperation,” the spokesman said.
"We will continue to build on the very strong relationship we already have with the US on defence and security matters."
Asked whether the Government was happy UK personnel had been involved in an operation where details had been shared with a journalist, the spokesman said he would not comment on intelligence matters.
Armed forces minister Luke Pollard told the Commons Defence Committee on Tuesday that no British service personnel had been put at risk as a result.
He added: "All UK service personnel are covered by our normal approach to operational security, and the committee will understand that I won't go into the details of how we keep our involvement in any support for military operations in the Red Sea or anywhere else (secure).
"But we've got high confidence that the measures that we have got with our allies, including the United States, remain intact."
The US National Security Council said the group chat "appears to be authentic", adding it was investigating how Mr Goldberg came to be included.
On Monday night, US president Donald Trump denied any knowledge of the breach, while a White House spokeswoman said the president retained "utmost confidence" in his national security team.
