Bulk access is necessary when, for example, the police service have identified one suspect in a paedophile ring and need to find out who they had been in contact with, which websites they visited and images they downloaded, he argued.
"That's when you need, as it were, the bulk access. You've got to get access to that information, some of which is historic. It's in the discovery of new leads that the bulk access to communications data is so crucial," he added.
However Omand admitted: "You really need to have a legal framework. As citizens we need to know how the law impacts upon us, and we have to be very confident that what is being done is in accordance with the law."
Omand currently serves as a commissioner for the Global Commission on Internet Governance and is a visiting professor at King's College London. He started his career at GCHQ and was director from 1996 to 1997. He served in senior positions at the Home Office, Ministry of Defence and Cabinet Office before retiring in 2005.
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