When the government passed laws authorising itself to snoop on all Internet traffic, some MPs asked if there couldn't be an exception for them, since after all certainly they aren't terrorists or paedophiles...
The response (IIRC from Theresa May who was Home Secretary at the time) was that this would be technically impossible.
The reason of course is that although the law is written in a way that suggests the letter authorising interception looks like "Dear Tiny ISP, you are required to store all the data about Bill The Terrorist so we can investigate very important crimes, love, the Home Secretary XX" the actual letters go like this: "Dear 10Tb/s Internet interchange, you are required to store literally everything, so that we can investigate whatever we want, love, the Home Secretary XX".
You could easily never issue letters requesting data for an individual MP, but if you never even intended to name individuals anyway then that's obviously not going to work...
Government secrecy should be absolutely restricted by the general public - it is the beginning of all corruption of government. The UK headed down the wrong path towards totalitarian class-ist society when it decided the common people shouldn't know their own governments' secrets.
Furthermore, it should be illegal for governments to use self-destructing messages.