Trying to claim the title for Edgar Wallace? :)
Edgar Wallace does take the title as far as I can ascertain as the writer of 'The Terror'.
This adaption of the Wallace play was first shown at the Piccadilly Theatre, London in October 1928 described with the banner "A Talking Film". Although it used the Vitaphone sound on disc system it was officially Britain's first 'all talking picture' (even going so far as to have the credits read aloud by a narrator) beating 'Blackmail' which was only just going into production.
Blackmail finally debuted in London in June 1929 but was even then being described as "the first full-length talking subject to be made in a British film studio".
Incidentally 'The Terror' also of course takes the title of Britain's first talking horror film. [/b]