British Prime Minister Tony Blair was told shortly after midnight that attacks on Iraq were being brought forward, his office said early this morning.
A British military spokesman at the US Central Command post in the Gulf said the British "were not expecting" the strike.
Mr Blair was told "attacks on a limited number of command and control targets were being brought forward" his Downing Street office said.
"As regards the involvement of British forces, the prime minister will set out the position in due course," the spokesman added.