What a lot of Discovery channels there are now on Sky Digital.
There's the original Discovery Channel. It's channel 520 on Sky. Also it's available on NTL 212, Telewest 212, and Top-up TV channel 27. Only right then that it be coded D1.
Discovery have put one other channel from their cluster on Top-Up TV DTT: Discovery Real Time on channel 28. In that case it should be coded D2.
There is also a Discovery Real Time Extra on Sky, but NOT Top-Up TV. Since it's an "extra" version of Discovery Real Time, let's code it D2X.
The other Discovery Channels are only on Sky and cable. They are best coded D followed by a letter. Here is my complete list of Discovery channels.
D1 = Discovery Channel (Sky 520, Top-Up 27)
D2 = Discovery Real Time (Sky 250, Top-Up 28)
D2X = Discovery Real Time Extra (Sky 252)
DA = (Discovery) Animal Planet (Sky 535)
DC = Discovery Civilisation (Sky 522)
DH = Discovery Home and Health (Sky 264)
DHD = Discovery HD (Sky 525)
DK = Discovery Kids (Sky 615)
DS = Discovery Science (Sky 523)
DT = Discovery Travel and Living (Sky 283)
DW = Discovery Wings (Sky 524)
Some of these also have +1 versions. To code these, append +1 to the matching code, e.g.
D1+1 = Discovery+1 (Sky 521)
DA+1 = Animal Planet+1 (Sky 536)