For info,
this is the official line from the Civil Aviation Authority (CAA) who make the regulations for the use of electronic equipment on aircraft. DVD players, along with most other electronic equipment are fine to use in-flight. They cannot however be used during taxy, take off or landing phases (below 10,000 ft), when seat belt signs are illuminated (eg when turbulance is expected) or when the commander of the aircraft (Captain) suspects the equipment is causing interference with aircraft systems.
Hope that helps!
Darren