### Clue: Downing Street leader's about to pursue German girl (9)
### Answer: INGESTION 
 ### Explanation: Definition: Downing
 [ ST(abbrev. for "Street") + **reversal of**(…'s about) [NO. 1](leader/chief, with the Roman numeral substitution) ] **placed below**(to pursue, in a down clue) INGE(a name for a German girl).
Defn: …, as a noun.