According to an ash forecast G was looking at yesterday, the cloud should move away from the South of the UK fairly quickly, so with luck they'll be delayed rather than have their flight cancelled.
G says that Eyjafjallajökull is capable of keeping this eruption going for the next 20,000 years, so this problem isn't going away any time soon and we might have to think of alternate ways of getting to Stockholm for our holiday in August.
We shall just have to wait and see. I find it slightly ominous that the BBC newsreaders have decided that it's worth learning how to pronounce it. :)