The prosecution has rebutted the argument that former Central Narcotics Bureau chief Ng Boon Gay has no case to answer, as the keenly-followed corruption trial resumed on Monday morning.

There was gratification obtained by Ng from former IT sales executive Cecilia Sue, said deputy public prosecutor Tan Ken Hwee. Referring to the defence's claim a fortnight ago that there was no gratification as the oral sex was not "completed", he added that this was mischievous.

District Judge Siva Shanmugam will decide after the prosecution and defence make their cases today whether Ng, 46, has a case to answer and hence take the stand, or acquit him.

Ng faces four counts of obtaining oral sex from Ms Sue last year in exchange for furthering the business interests of her IT firms.