LONDON - If you get a letter from Britain's No 10 Downing Street, don't bother with a personalized response. The person who signed it probably used a fake name.

For years, staff at the British prime minister's office have been using bogus names in their correspondence with members of the public, Downing Street acknowledged in a statement Wednesday.

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It said that use of pseudonyms was introduced in 2005, after an official was tracked down by a constituent she'd been in contact with and threatened at her home address.

But the practice didn't become known until a long-serving member of Parliament, Gerald Kaufman, told fellow lawmakers in the House of Commons that he'd received a message from a certain "Mrs. E. Adams" in Downing Street's direct communications unit.

When Kaufman tried to get in touch with Adams, he was at first told that she didn't speak on the phone. Eventually, he was told she didn't exist.

"What extraordinary events are taking place in 10 Downing Street whereby they send letters from somebody who doesn't exist and expect one to accept this?" Kaufman said.

The letter, complete with the bogus signature, was later broadcast on Britain's Channel 4 News and carried on the BBC website.

A (real) Downing Street official said in an emailed statement that while the prime minister's office was looking in to alternatives to the use of pseudonyms, "we are clear that our priority is the security of our staff."