Iranian Kidnappings

I'm not quite sure what to make of this, and would appreciate a few idea's about what Iran hopes to achieve by these actions.
I'm pretty sure it's not just a practical joke.
So what are their aims?
Do they seek to try and humiliate the western forces in the region?
Are they making an attempt at solidarity with Iraq and other nations in the region?
Do they want to be pro-active in showing that they won't be pushed around? (with regard to the so-called "axis of evil)
Is it realpolitik, and they are getting tough to show that they will do what they want (with regard to the alleged development of nuclear weapons)

It's kind of confusing as unless Britain just totally backs down, they are in a no win situation....

Any serious thoughts would be much appreciated