I think that is where the abilities of the authorities is going to fall down. Unless the UK gov has a few 0days to share to the world I could imagine that a lot of this could come down to client-side attacks and phishing, which may fall under entrapment (IANAL). Or some imaginative MitM through insecure or badly configured wireless in more complex cases.
I'd like to see what they intend to throw at the machines to 'investigate'.
But my main concern is that they feel this is acceptable. Whilst a comment to the original article claims that police in the UK have had these powers for awhile and the only change is sharing data with the EU (IANAL so I can't say if this is the case or not), I don't see how anyone can believe, following recent high profile issues that these powers will not get abused. Supposedly the powers are only available if a superior offices deems them accused crimes to be relevant to a minimum crime (3months jail time I think), who confirms if the superiors' belief was correct. And surely if the accusation warrants the penalty a judge would see it the same way and provide the warrant.
I've got no complaints with providing the authorities the ability to conduct investigations; but there must be sufficient checks and balances in place to ensure the power isn't abused. As an example (can't find my link) some councils in the UK have used recent 'terrorist' surveillance provisions to monitor which residents put their bin out the night before collection day.
Why not have the ability in place, providing a judge agrees and provides the warrant?
Additionally, what happens if the authorities 'search' a PC for an individual accused of a crime that warrants the search and they find no evidence of the original crime, but find evidence of a lesser offence? is the evidence still valid despite being gained through the backdoor?
How can the authorities ensure, 100%, that their searches will have no negative impact to the working of an innocent persons private property (I think we're still innocent until proven guilty aren't we?...)
How can the authorities ensure, 100%, that no 'remains' will be left in the system following their intrusion. McKinnon supposedly did no damage to the systems he connected to, but the US government claim the clean-up bill was huge because they couldn't ensure that there wasn't something on the systems that they had missed. If the US can't prove this, how can an individual with a home PC?
I think these, and many more, questions need answering
</rant - sorry folks....>