Twenty three expelled Russian diplomats and their families left the embassy in London and headed back to Moscow on Tuesday in the deepest crisis in Russian-British relations since the Cold War sparked by a nerve agent attack in England.
Prime Minister Theresa May blamed Russia for the attack on a Russian double agent and his daughter - the first known offensive use of a nerve toxin in Europe since World War Two - and gave 23 Russians whom she said were spies working under diplomatic cover one week to leave London.
Russia has repeatedly denied any involvement in the attack on Sergei Skripal and his daughter and on Saturday gave 23 British diplomats a week to leave Moscow as well as closing the British Council in Russia.
Three buses with diplomatic number plates left the Russian embassy compound in London on Tuesday morning, a Reuters photographer at the scene said. Embassy workers waved to the leaving diplomats as the buses pulled away. One diplomat held a pet in a cage.
READ: UK to expel 23 Russian diplomats following nerve attack on double agent
As the diplomats leave London in the biggest tit-for-tat expulsions since Margaret Thatcher ordered Soviet spies to leave in 1985, May was due to chair a National Security Council meeting on the crisis.
Russia has refused to explain how Novichok, a nerve agent first developed by the Soviet military, was used to strike down Skripal, a former colonel in Russian military intelligence who betrayed dozens of spies to Britain.
Skripal, 66, and his 33-year-old daughter Yulia have been critically ill since they were found unconscious on a bench in the English city of Salisbury on March 4. A British policeman who was also poisoned is in a serious but stable condition.
Russia says it knows nothing about the poisoning and has repeatedly asked Britain to supply a sample of the nerve agent that was used against Skripal.
The United States and European powers say they share Britain's belief that Russia is culpable for the poisoning though they given no indication of what they will do about it.