With the Ash Cloud from Iceland grounding flights until Saturday at the earliest, I thought I'd show you an animation of the ash cloud moving across from Iceland. The Image here is false colour, and is done by looking at particular wavelengths in the infra-red, which allows the ash to be differentiated from cloud. The images are all from Eumetsat.
The ash cloud was formed when Eyjafjallajökull erupted under a glacier. The glacial ice melted, and rushed out to scrape the nearby landscape (which makes for an eery drive, I'd been to that area a couple of times pre-eruption - and annoyingly, I've just noted I never finished writing up my last trip!)
The cloud does look pretty diffuse for the UK, but I suppose they're acting on a precautionary principle.