GCHQ already monitors tinternet, so the national security thing is already covered.
We wouldn't agree to all our mail that receive and send being opened by the Post Office, and all information therein being recorded. It would be an invasion of privacy. This is just an electronic version of reading our letters and is an invasion of privacy.
No doubt we will get the usual nonsense replies that it should be allowed because if you nothing to hide, you have nothing to fear. Law abiding people are entitled to their privacy, and being electronically tagged when you have not done anything wrong, is draconian.