Nicholas Elliott, 77, the British agent who confronted his colleague Kim Philby with evidence he was a Soviet spy, died of cancer Wednesday in London.

As an agent for Britain's foreign intelligence agency, he defended Mr. Philby when suspicions were raised in the 1950s. Mr. Philby was cleared in 1955, but confessed when conclusive evidence came to light and Mr. Elliott confronted him. Mr. Philby then fled to Moscow.