The US and UK are to wage a series of cyber 'war games' against each other to test the resilience of the two country's defences against online criminals, beginning with a mock exercise directed at the banking and finance sector.
The joint initiative was unveiled by David Cameron's office as the UK Prime Minister begins two days of meetings with President Barack Obama in Washington.
Unnerved by the recent North Korean hack on Sony, Downing Street said the unprecedented exercise will aim to improve the flow of information between the US and UK about emerging cyber threats.
Under the plans, the US and UK will create a joint 'cyber cell' for information exchange between the FBI and UK security services, including MI5 and GCHQ.
The first of the war games will take place later this year, with the Bank of England, and banks in the City and on Wall Street in the firing line.
While in Washington, Cameron is also expected to press Obama on proposals to open a back door to get around the encryption defences erected by big technology companies to protect consumer data, a plan which has caused consternation in hi-tech circles in the UK.