Britain would revoke the accreditation of a Russian diplomat and a diplomatic spouse in response to a similar action taken by Russia earlier this week against British diplomats, the Foreign, Commonwealth and Development Office said in a statement on Wednesday.
"It is clear that the Russian state is actively seeking to drive the British Embassy in Moscow towards closure and has no regard for the dangerous escalatory impact of this," the statement said.
"We do not take this decision lightly, but we have always made clear to Russia that if they escalate, we will take reciprocal action," it added.
The move follows Russia's announcement on Monday that it would expel two British diplomats, accusing them of "providing false information and conducting intelligence and disruptive activities."