Theresa May has urged Britons not to allow the terror attack on a German Christmas market to stop them enjoying the festive season as usual.
The Prime Minister said it was important for the UK to send out a message that "we will not be cowed by the terrorists".
Police in Germany are hunting a Tunisian man suspected of driving a truck into crowds at the market in Berlin on Monday, killing 12 people and injuring 48.
Speaking to the Evening Standard, Mrs May said concern over the incident should not deter people from getting on with usual visits to shops and entertainment venues in London.
"Of course our thoughts are with those who have been affected by the terrible attack that took place in Berlin but Londoners should go about their business as usual," she said.
"They should enjoy this Christmas period.
"It is important, I think, that we send a very clear message that we will not be cowed by the terrorists - that we will carry on with our lives as usual."
The Prime Minister paid tribute to Britain's security agencies and police for the work they do keeping the public safe from terror attacks, hailing them as "unsung heroes".
MI5 chief Andrew Parker said last month that 12 potential attacks had been thwarted in the last three years.
Mrs May said: "The security services and the police are working day in and day out to keep us safe.
"They are often unsung heroes but they are actually doing a very good job. However, they have to be vigilant all the time and we should be very grateful for the work they do."
Relatives of prime suspect Anis Amri have urged him to turn himself in to police.
Amri, who turned 24 on Thursday, is understood to have left Tunisia in the wake of the 2011 Arab Spring uprising and spent time in Italy before entering Germany last year.
His asylum claim was rejected and authorities identified him as a threat before the Berlin outrage.
His brother Abdelkader Amri told the Associated Press: "I ask him to turn himself in to the police. If it is proved that he is involved, we dissociate ourselves from it."
German authorities issued a wanted notice for Amri on Wednesday and have offered a reward of up to 100,000 euro (£84,000) for information leading to his arrest.
Meanwhile, the Christmas market has reopened to the public with additional security measures.