Dylan Earl, 20, appeared in a London court on Saturday charged with two offences under the National Security Act in relation to "activity likely to benefit Russia", according to court records.
Earl was also charged with arson in relation to a commercial premises in London.
Two other men, Paul English, 60, and Nii Kojo Menash, 21, have also been charged with arson.
Britain's Crown Prosecution Service said in a statement the arson charges related to "an arson attack on a Ukrainian-linked commercial property in March 2024".
Two further defendants appeared at London's Westminster Magistrates' Court on Friday.
Jake Reeves, 22, was charged with agreeing to accept a material benefit from a foreign intelligence service and arson.
Dmirtrijus Paulauskas, 22, was charged with failing to disclose information to police about terrorist acts.
Prosecutors said the charges against Reeves and Paulauskas were linked to the investigation into Earl, English and Mensah.
The five men will appear in court at the Old Bailey on May 10.
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