so I cannot comment on the Dutch case.
There are some general details here on the associated subject of self incrimination here :
http://en.wikipedia.org/wiki/Self-incrimination Looks as though in the UK they would have the right to silence.
Non attendance, if called, could cause a case to collapse. I doubt they'd get away with non attendance here given that some / most of the trials will be interdependent on each other. That is even to the extent they've already said there will be a complete media lock down on court evidence at the trials when they do start, expected to be in a block during the spring of 2013 , publication of which could be subjudice with respect to another trial.
The Guardian was caught out in one specific incident for which they may have been set up - they published the name of someone arrested before the information had been released and a Met police officer was arrested almost immediately. All of our newspapers knew that the Guardian had had someone "inside" since at least February this year that being the only explanation for their scoops.
We'll have to wait and see. If the police officer incriminates the reporters they're screwn anyway.