Jason Flemyng was cast as
Quatermass, with long-time Kneale admirer
Mark Gatiss as Paterson,
Andrew Tiernan as Carroon,
Indira Varma as his wife Judith,
David Tennant as Briscoe,
Adrian Bower as Fullalove and
Adrian Dunbar as Lomax—as a Ministry of Defence official rather than a policeman.
Isla Blair was cast as Home Secretary Margaret Blaker, a combination of parts of Lomax's character and two officials from the original serial, and she brought to
rehearsals a photograph of her husband
Julian Glover on the set of the 1967 film version of
Quatermass and the Pit. Blair said that she was delighted to be joining "the Quatermass club". Original 1953 cast member
Moray Watson, who had played Marsh, one of Quatermass's colleagues, visited the set during rehearsals. The 76-year-old was invited to make a
cameo appearance in the live broadcast, but was not available that evening. It was during the rehearsals for
The Quatermass Experiment that David Tennant was offered the role of the
Tenth Doctor in
Doctor Who. This casting was not announced to the public until later in April, but his fellow castmembers and crew became aware of the speculation surrounding Tennant; in the live broadcast Jason Flemyng changed Quatermass's first line to Tennant's Dr Briscoe from "Good to have you back, Gordon" to "Good to have you back, Doctor" as a deliberate reference. ==Production==