What about the Data Protection Act and the FCA
The DPA mentions encryption quite often which means we will be in breach of either this regulatory law or whatever law the government decides to bring in forcing us to not protect the sensitive data.
Cameron is probably thinking we can have a completely separate consumer and enterprise device ecosystem and that no terrorist will use a business or rooting to get access to encryption.
I don't see what good this will do when the current regulation already lets the state lock you up until you give up your encryption keys.