Only in the 1970s did the first accounts emerge and the full significance of "the most successful intelligence agency in world history" gradually become apparent. This is all the more remarkable, given the scale of operations at BP. At times, around four thousand high-grade German signals were read a day, many within 24 hours of being intercepted. This was achieved by "an extraordinary mixture" of people, drafted in from all walks of life, civilian and military. At its peak, perhaps 10,000 people worked at BP; but for decades no-one talked publicly about their experiences. Only in 1993 did Hinsley and Stripp's Codebreakers give details of 'the inside story of Bletchley Park'. Much, of course, remains to be told. ..