Always remember

The UK government, advised by malign and/or stupid people in the intelligence services, is not on your side.

Anyone who actually has anything to hide will be using a third-party solution already: all this achieves is making it easy for some creepy voyeur in the intelligence services can look at, for instance, the photos taken by a large number of innocent people.

For messaging, such third-party tools will already run in browsers: bad people will already be using them. This is targeted entirely at innocent people.

(I have nothing to hide, have no compromising photographs, and I already use a third-party solution for encrypted backups. So should you.)