Some of London's prominent landmarks will tonight light up in blue, white and red - the colours of the French national flag - to pay tribute to the 17 people killed in the Paris terror attacks.
The famous Tower Bridge, Trafalgar Square and National Gallery in central London are to be lit up with blue, white and red colours.
The show of solidarity will coincide with British Prime Minister David Cameron's visit to Paris to join other world leaders for a mega unity march.
UK Home Secretary Theresa May has also joined EU interior ministers at a meeting to discuss the response to the attacks.
Eleven people were killed by al Qaeda terrorists at the offices of the satirical magazine 'Charlie Hebdo' on Wednesday, besides two policemen.
Four hostages died at a Jewish supermarket on Friday.
Cameron earlier tweeted to say he was on his way to Paris to "march with the French people".
"The #CharlieHebdo murders will not crush our spirit or our values," he said.
Labour leader Ed Miliband, who is also going to Paris, said: "All of us have been shocked and appalled by the events in France, by the murderous terrorism that this represents.
"We've been inspired by the response of the French people, and indeed by the response of people across faiths, across communities, in this country."
French Ambassador to the UK Sylvie Bermann said she was grateful for Britain's show of solidarity.
"A lot of people also came to the embassy and signed our condolence book and also sent flowers - like the mayor of London - and I understand that (Deputy Prime Minister) Nick Clegg will participate in our rally in Trafalgar Square," she said.
