Air Traffic over Britain, courtesy of the BBC. Except when it isn't, courtesy of Eyjafjallajökull.
Looks like I'll be rescheduling that London trip again, given that, according to the Times:
The perfect combination of calm atmospheric conditions and unrelenting activity of the Eyjafjallajökull volcano means that the cloud could loom over Britain until late next week.
While there could be brief spells when the plume clears parts of the airspace, it is not certain that these will be long enough for airlines to resume flights.
This would be the same trip that I rescheduled in September when I came down with the flu, and picked April 22nd at random, because April seemed like a good time to go to London.
Except when volcanoes blow.