The FSB security service said the diplomat, whose photo was splashed across TV news bulletins, had intentionally provided false information when he entered the country.
“At the same time, the Russian FSB has discovered signs of the said diplomat conducting intelligence and subversive work that threatens the security of the Russian Federation,” it said in a statement.
There was no immediate comment from Britain’s Foreign, Commonwealth and Development Office. The British embassy in Moscow did not respond to a request for comment.
The TASS news agency cited Russian Foreign Ministry spokeswoman Maria Zakharova as saying that the ministry had summoned the British ambassador, a step that host governments often use to express a strong protest.
According to the FSB, the British diplomat was a replacement for one of six UK diplomats expelled earlier this year, also on espionage charges.
Relations between Britain and Russia have plunged to post-Cold War lows since the start of the Ukraine war. Britain has joined successive waves of sanctions against Russia and provided arms to Ukraine.
Russia said Ukraine fired British Storm Shadow cruise missiles at its territory last week for the first time. President Vladimir Putin cited that, and the launching of US ATACMS ballistic missiles by Ukraine, as the reason Russia responded by launching a new hypersonic missile at the Ukrainian city of Dnipro on November 21.
