Alternatively (and more likely I suspect), these is some gamesmanship being played to get shiny new additional super-snooping laws passed because it's needed to cope with all this uncrackable terrorist encryption. See, here's the proof it exists ! [edit: sorry, this did not make it clear I'm suggesting it was cracked but found to be irrelevant to the terrorism case. I've expanded in a reply below.]
The UK already has laws making it an offence to have 'have information' 'which may be of use to anyone planning a terrorist offence'. This is so broadly defined that railway enthusiast pictures of trains could fall into it (and have been questioned under it - http://www.telegraph.co.uk/news/uknews/road-and-rail-transpo...)
The UK's unwritten constitution is not worth the paper it's written on. Unfortunately the US written one seems to be about as useful in protecting peoples rights these days as the UK one. (See previous HN stories of your choice)
GCHQ have considerable computing power. That probably has weird costings. Thus the cost of 48 hours to run this task is possibly costed at some huge amount that police forces cannot afford unless they know it is a significant target with a spectacular result.
Remember this was originally a terrorist case; there would have been plenty of resources made available - there always are for these.
A likely scenario is it was cracked and found to be irrelevant so the option of going for a political angle for more powers was much more preferable than letting some low-level frauster know his encryption had been cracked (and hence letting lots of people know the USB encryption was worthless and risking real terrorist cases where suspects used the same approach).
Just wow! Does that include engineering books?
Under the Regulation of Investigatory Powers Act 2000[1] it doesn't matter whether you forgot a password or not. Failure to provide it is against the law.
This Act has proved highly controversial for a number of reasons. The potential for fitting someone up by claiming that they aren't disclosing a password that in reality they can't disclose was one of the civil liberties concerns expressed even before the Act was passed.
[1] https://en.wikipedia.org/wiki/Regulation_of_Investigatory_Po...