Yelena Tregubova, 34, said by telephone from London that her life would be in "grave danger" should she return to Russia.
"I can't say much, except that going back to Russia would be a big mistake," Tregubova said.
She declined to say who might be behind any threats against her.
Published in 2003, Tregubova's book, "Tales of a Kremlin Digger," chronicles her experiences covering the Kremlin for several national newspapers from 1997 to 2001. It contains juicy accounts of private episodes, such as a dinner with then-FSB director Vladimir Putin, and criticizes the Kremlin for curbing press freedom after Putin became president.
In February 2004, a small bomb exploded outside Tregubova's apartment on Pushkin Square, smashing several lampshades and a windowpane in the stairwell. Police said it was an act of hooliganism, though Tregubova said she believed she was the target.
Tregubova said she arrived in London to visit friends in January 2007. During that visit, it became clear that any return to Russia would put her in "mortal danger," and she has not left Britain since, she said.
She said she applied for political asylum with British Home Office, which handles immigration affairs, in April 2007.
A British Embassy spokesman said Britain could not comment on individual cases.
A Foreign Ministry spokesman declined to comment immediately on Tregubova's case.
Tregubova covered the late former President Boris Yeltsin and then Putin for Kommersant, Izvestia and Russky Telegraf from 1997 to 2001.
In her book, she writes that, shortly after Putin came to power, the Kremlin pool of reporters saw a wave of repressions in which those who did not toe the official line -- including herself -- lost their accreditation.
After the murder of journalist Anna Politkovskaya in October 2006, Tregubova wrote an open letter to Western leaders, including German Chancellor Angela Merkel, in which she called on them to demand that Putin stop political murders, human rights abuses and restrictions on the press.
Tregubova joins several other Russian political refugees currently living in Britain, including businessman Boris Berezovsky, Chechen rebel envoy Akhmed Zakayev and Marina Litvinenko, wife of former Federal Security Service officer Alexander Litvinenko, who died in 2006 after ingesting radioactive polonium-210.
Tregubova said she was currently writing another book, the details of which she declined to discuss.
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