BBC Cast List

The following is the cast list (as far as I know it at the moment) for the BBC series.

Lady Gertrude - Celia Imrie
Dr Prunesquallor - John Sessions
Barquentine - Warren Mitchell
Lord Groan - Ian Richardson
Fuchsia - Neve McIntosh
Nannie Slagg - June Brown
Flay - Christopher Lee
Swelter - Richard Griffiths
Steerpike - Jonathan Rhys Meyers
Clarice - Zoe Wanamaker
Cora - Lynsey Baxter
Irma Prunesquallor - Fiona Shaw
Bookman - George Viasoumi
Keda - Olga Sosnovska
Mollocks - Eric Sykes
Poet - Sean Hughes
Rottcodd - Windsor Davies
Titus - Cameron Powrie / Andrew Robertson
Professor Bellgrove - Stephen Fry
Professor Perch - Mark Williams
Professor Fluke - James Dreyfus
Professor Shred - Phil Cornwell
Professor Mule - Steve Pemberton
De'ath - Spike Milligan
The Fly - Gregor Fisher
Doggit - Lewis Rose
Boatman - Tim Barlow
Wild Girl - Caroline Nelson / Daniela Zocchi

Notes

De'ath is in fact the headmaster, Deadyawn, under a different name.
Rottcodd's name has been used for a new character -- the Rottcodd of the books does not appear.