For starters, the couple could have used stress-tested PGP (Pretty Good Privacy) for point-to-point encrypted email which involves installing a separate piece of client software and the exchanging of publickeys.
Their main fear is the ease with which police would be able to gain access to the publickeys lodged with Trusted Third Parties, posing a threat to privacy and individual liberties.
The Confederation of British Industry has said it is concerned about the licensing scheme being proposed, where Trusted Third Parties will handle digital signatures and hold the publickeys that can unlock encrypted communications.