The sex-for-grades trial resumed this morning with law professor Tey Tsun Hang cross-examining the anti-graft investigator who recorded his statement last year.

Tey, who is facing six charges of corruptly obtaining gifts and sex from former student Darinne Ko Wen Hui, is defending himself in court.

The tense exchange between him and the Corrupt Practices Investigation Bureau's (CPIB) Bay Chun How, was played out in a trial within a trial to determine if Tey's statements can be admitted as evidence.

Tey, 41, alleged in court on Thursday that he had been badgered and verbally abused by Mr Bay.

These acts, such as an alleged threat to place Tey's wife under arrest, took place during Tey's time with Mr Bay in April last year.

Tey also claimed that he had been under psychoactive medication and had made his first confession on April 5 under duress.

He also claimed he had been held in a 'very cold cell' on April 2.

Mr Bay, however, disagreed with each of Tey's accusations and maintained that he had given Tey the option to make his April 5 statement at another time.

When Tey alleged that he had been held on April 2 in a "very cold interrogation cell", Mr Bay replied: "'The air-con controller was mounted on the wall for you to adjust."

In another instance, Tey said that contrary to Mr Bay's testimony on Wednesday, his father was not watching television when CPIB officers went to Tey's home to pick him up, to which the CPIB officer replied: "The defendant's father was on a wheelchair, facing the television. The television was on. I would not know if he was watching or not."