We could make it mandatory for corporations providing message-decrypting to the security services to charge £100,000 for each person monitored in a given calend

We could make it mandatory for corporations providing message-decrypting to the security services to charge £100,000 for each person monitored in a given calendar year. Easily affordable for genuine ticking time-bombs and terror threats - but too expensive for spies to stalk their ex-girlfriends or track everyone at a large protest.