It's great that Cameron is quoting Shakespeare. It reminds me that one of the most subversive things that Shakespeare does is put fine words into the mouths of unpleasant people. Here's the 'usurper' Henry IV, who has used people to help him seize the throne and kill the previous king:
"How now, my Lord of Worcester? 'Tis not well
That you and I should meet upon such terms
As now we meet. You have deceived our trust
And made us doff our easy robes of peace
To crush our old limbs in ungentle steel."
Dear oh dear, poor Henry - having to face the very same kind of rebellion (barons rising up against the king) as he organised himself. Note the pompous 'deceived our trust' - which is precisely what he himself did.