The Paris attacks - Sir Bernard Hogan-Howe.
Sir Bernard Hogan-Howe has sent his condolences and offered his support on behalf of the service.
The Commissioner said:
"My thoughts, and those of Met officers and staff, are with Paris and the men and women whose job is to deal with this horrific situation.
"London and Paris are linked as two of the world's strongest capital cities and we stand prepared to help in any way.
"We have developed appropriate tactics to deal with a firearms attack in London, but we will, of course, urgently review our approach in the light of last night's act of terrorism in Paris. The scale of the attacks and the range of weaponry used by the terrorists are a serious cause for concern. But the public can be reassured that our firearms officers are trained to deal with this kind of incident and we are constantly evolving new ways to combat the threats to public safety."
The UK Government recognised the increased threat in the summer of 2014 and raised the threat level to a point where an attack is considered to be highly likely.
Police and security agencies have been working flat out since then to protect the public. They are currently working on hundreds of active investigations and making, on average, an arrest a day.
Additional high-visibility patrols are in place to provide reassurance at key locations across the Capital. Officers are working closely with London's communities and businesses to offer reassurance and advice following the horrific attack in Paris.
Assistant Commissioner Mark Rowley, National Police Chiefs' Council lead for counter terrorism, said:
"The ambition of terrorists is to sow discord, sow distrust and create fear. But at the heart of success in countering terrorism, regardless of the operations we run and the arrests we make, is the relationship between the public and the police. It needs to be stronger than ever.
"In particular, we as the police depend massively on information from communities; whether it's about suspicious individuals or suspicious behaviours. We've had more reports than ever before over the last year. That needs to continue."
"We are reviewing our police stance across the country, but however strong we are, however ready we are, regardless of how many people we are arresting; we will be dependent upon the confidence and strength of communities to work with us."
Speaking about changes to policing, he added:
"We have been strengthening our policing at ports and we have been strengthening policing on the street. People may notice some changes at events at big cities across the country.
"We will constantly keep that under review in the forthcoming days and weeks but we can't let the terrorists defeat us by becoming fearful and withdrawing from the streets.
"The term I would use is 'to be alert, not alarmed'. People should recognise that we have been talking publicly about our efforts to counter terrorism and we have seen a positive response from the public over the last year.
"It comes down to trust between communities and that ability for the public to trust the police, work with us and supply us with the sort of information that they have been doing."
Speaking about the current threat level and responding to an attack AC Rowley added:
"The threat level is currently at 'severe' which means an attack is highly likely - that's the assessment which we have prepared for. For example people would have seen the large-scale training held in London this summer, for the type of scenario that tragically happened in Paris in the last 24 hours.
"We have been planning for it and it's very much on the radar in terms of something that we fear may happen, but of course we constantly hope it won't happen.
"So we are doing everything we possibly can do and of course there are no guarantees. But I would come back to the relationship between the police and the public and the amount of information which has been fantastic recently. We need that to continue, because it is that vigilance which gives us the first insight into a possible attack."
The public is asked if they see or hear anything suspicious to contact police or the confidential Anti-Terrorist Hotline 0800 789 321.