Nick Heath at ZDNet reported that earlier this morning the UK National Air Traffic Service suffered an outage that affected many southerly routes across the country. Heath was tipped off to the problem by a tweet from David Kaminski-Morrow. As Heath puts it,
The technical issues were triggered by a "problem with a flight plan" entered into a system according to a spokeswoman for NATS.
The problem was resolved after a short time, but a backlog of flights resulted. GlitchReporter suspects either software test failure, or a related lapse in data quality.