I'm entirely against what the UK government wants, however I would say:
Although you're right that tech people would still be able to choose secure encrypted options, the fact is that the majority of criminals by pure numbers are not very sophisticated - so while this sort of backdoor obviously wouldn't be a guarantee that every criminal conversation could be snooped on, it would work on the 90-99% (I'd guess towards 99) who aren't both cautious enough to try to be secure and tech savvy enough to make the right choices.
(But it's still a terrible idea, both for the sake of general privacy principles, and for the risk that current or future governments or personnel will abuse the access, and for the risk that criminals outside government will be able to take advantage of the same backdoor.)
Although you're right that tech people would still be able to choose secure encrypted options, the fact is that the majority of criminals by pure numbers are not very sophisticated - so while this sort of backdoor obviously wouldn't be a guarantee that every criminal conversation could be snooped on, it would work on the 90-99% (I'd guess towards 99) who aren't both cautious enough to try to be secure and tech savvy enough to make the right choices.
(But it's still a terrible idea, both for the sake of general privacy principles, and for the risk that current or future governments or personnel will abuse the access, and for the risk that criminals outside government will be able to take advantage of the same backdoor.)