Tory leadership race: Date when new Prime Minister will be named is revealed
He said nominations to be leader of the Conservative Party, and therefore prime minister, will close on Tuesday.
The names of the proposer and seconder will be made public.
Candidates must win at least 30 votes from party colleagues to progress.
A second ballot is planned for Thursday.
If the number of candidates has not then been narrowed down to two, ballots are expected to begin again on Monday next week.
Sir Graham said the new leader would be announced on September 5 but would not say when the final vote would take place.
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