During the 1950s and 1960s, a large number of MI5 operations failed in circumstances that suggested the Soviets had been tipped off. Although many such failures were subsequently blamed on the actions of such self-confessed or defected agents as Philby, Guy Burgess, and Anthony Blunt, a number of failures occurred after all three had lost their access to secret information. Some in MI5 concluded the Soviets had an agent in a very senior position within the organisation. Peter Wright, Arthur S. Martin, Jane Sissmore and others became convinced that either Hollis or his deputy, Graham Mitchell, could be the only ones responsible, eventually confiding their suspicions to Dick White, director general of MI6. White instructed Martin to inform Hollis that Mitchell was a suspect, and Hollis instructed Martin (after due consideration) to keep Mitchell under surveillance. Author Nigel West implies that this was a deliberate ploy to keep tabs on both Mitchell and Hollis.