Diplomatic vehicles drove them from the embassy in London to Stansted Airport, where they boarded a plane to Moscow.
The UK expelled 23 diplomats after Prime Minister Theresa May said Russia was “culpable” for the poisoning of Sergei Skripal and his daughter.
The government decided on Tuesday not to impose further sanctions on Russia for now.
However, at a meeting of the National Security Council, Mrs May said: “There are other measures that government and security officials are actively considering and stand ready to deploy at any time.”
Strict checks by border officials on private flights have been introduced as the UK increases efforts to monitor and track those entering the country, Mrs May’s spokesman added.
Moscow has denied all involvement, and is expelling 23 British diplomats in response. The UK diplomats have until Saturday to leave Russia.
The Kremlin is also closing down both the British Council in Russia, which promotes cultural ties between the nations, and the consulate in St Petersburg.
The Russian foreign ministry, meanwhile, has invited all foreign ambassadors in Moscow to a meeting on Wednesday to clarify the Russian position on the Skripal affair, the Russian news agency Interfax has reported.
The Russian Embassy in London said around 80 people – including the Russian intelligence officers and their families – were due to leave the UK on Tuesday, the deadline given by Mrs May.
A small crowd gathered outside the embassy and waved goodbye to people carrying suitcases, children and pets as they boarded vehicles.
Russian ambassador to the UK Alexander Yakovenko tweeted: “Today we bid farewell to our colleagues heading home after the hostile move of the UK Government, and wish them all the best in their careers.”
The BBC’s diplomatic correspondent James Robbins said launching further measures “risks an endless tit for tat with the Kremlin”.
But “not to do so risks accusations of weakness from some quarters,” he added.