She said that Britain shared the concerns of the US that other nations were failing to invest enough and "share the burden", adding: "It is only by investing properly in defence we can ensure we are properly equipped to face the challenges."

Britain and the US would "work closely together to defeat Daesh", she said as she pledged to deepen "intelligence and security co-operation" and hinted at a new drive to defeat Daesh on the internet.

She said: "We are discussing how we can work even more closely together in order to take on and defeat Daesh and the ideology of Islamist extremism wherever it is found."

Russia

The press conference highlighted the stark differences between Britain and the US on Russia.

Mr Trump refused to be drawn on suggestions that his administration would lift sanctions on Russia, saying that it was "very early to be talking about that".

Mrs May said she supported continued sanctions on Russia, and had advocated for that policy within the European Union.

Mr Trump went on to say that while he hoped he had a "fantastic relationship" with Vladimir Putin, the Russian President, although he might come to find that he didn't like him.