British PM David Cameron, has warned "we must be prepared for a number of British casualties" after nearly 130 people died in the "brutal" attacks in Paris.
Cameron is reported to have convened a Cobra emergency response committee meeting on Saturday, where he hinted Britain's terror threat level remained at "severe", but the Paris attacks which have taken the world unawares would prompt a review.
The UK PM also said "however much we prepare, we in the UK face the same threat" and sympathized with France who came under attack on Friday evening as a series of attacks were carried out across Paris, reportedly by eight gunmen and suicide bombers believed to have been carried out by ISIS terrorists who described the tragic event as ‘act of war’.
The attacks left about 120 people killed and 280 critically injured with scores of people still searching for relatives.
Islamic State militants have claimed responsibility of the savage attacks, and Mr Cameron, obviously wary of developments, said it showed the threat from the group was "evolving", with a "new degree of planning and co-ordination and a greater ambition for mass-casualty attacks".
He added: "The terrorists' aim is clear: it is to divide us and to destroy our way of life. So more than ever we should come together and stand united and carry on with the way of life that we love."
Meanwhile, Britain’s Foreign Office said it was "urgently investigating" whether any British nationals had been caught up in the attacks and asked people with concerns about British relatives or friends in Paris to call 0207 008 0000.
As a sign of solidarity, Tower Bridge in London is to be lit up in the colours of the Tricolour later as flags are being flown at half mast at Downing Street and the French Embassy in London, with a vigil planned in Trafalgar Square later.
Groups who would like to take part in the vigil include the Muslim Council of Britain and the Christian-Muslim Forum.
The UK police have also assured there would be strengthened policing at ports and more police at public events in the coming days.
Sir Bernard Hogan-Howe, the Metropolitan Police Commissioner said police would "urgently review" tactics to deal with firearms attacks in light of the Paris killings.
British police have confirmed Gatwick Airport's North Terminal has been evacuated and they are dealing with a "suspicious package".
Officers said a man who "discarded an item at the airport" had been arrested and the issue being studied.
A state of emergency has been declared in France.