Then again, continued Poirot, "at the beginning, did I not repeat to you several times that I didn't want Mr. Inglethorp arrested now? 
Poirot did want Mr.Inglethorp to be arrested at a later stage. 
mnli hypothesis: Poirot did want Mr.Inglethorp to be arrested at a later stage.  premise: Then again, continued Poirot, "at the beginning, did I not repeat to you several times that I didn't want Mr. Inglethorp arrested now? 