A new exhibition at the National Archives in London will reveal the extent of MI5 operation to expose the British double agent who was also Observer reporter

Secret surveillance of Britain’s ­notorious double agent, Kim Philby, made public for the first time in archived documents, reveals how keenly the Security Service wanted to confirm or disprove early suspicions of his high-level treachery.

In daily bulletins submitted to MI5 in November 1951, undercover operatives describe how Philby, codenamed Peach, moved about London.