Clue: Rising cheer welcoming politician's preparation to speak (8)
Answer: HARRUMPH
Explanation: Definition: preparation to speak
An envelope ('welcoming') of MP ('politician') in HARRUH, a reversal ('rising' in a down light) of HURRAH ('cheer'). I associate HARRUMPH with an expression of disapproval, but it is a clearing of the throat, which may be a 'preparation to speak'.