Scaramella, who is believed to have close ties to Russia's secret services, is under the protection of British police and will reportedly be questioned.
Litvinenko died on November 23 after being poisoned with polonium-210, a highly radioactive element.
British Prime Minister Tony Blair today told a news conference in Copenhagen today that Litvinenko's death was a "very, very serious matter." He promised a thorough police investigation and said he would raise the issue with Russian President Vladimir Putin.
Russia denies involvement in Litvinenko's death.
Russia's Prosecutor-General's Office today said it is ready to assist London's Scotland Yard in its investigation.
(Reuters, AP, AFP, Interfax, ITAR-TASS)