A twist emerged in the sex-for-grades corruption trial on Tuesday morning when the NUS law professor at the centre of it produced a cheque book entry showing a sum of $2,500.

Tey Tsun Hang claims he had given this to former student Darinne Ko in July 2, 2010, and suggested it was payment for the items she had given him and the dinner she had paid for. Ms Ko flatly denied having ever received it.

Tey asked the court to grant an application to have the entry admitted for forensic ink dating and handwriting checks. The prosecution strongly objected to this, arguing that it was a "smokescreen to distract the court".

The cheque was dated July 2, 2010 but included payment for the dinner on July 8, 2010. The prosecution said Tey had a "remarkable ability" to predict future events.

The judge has yet to make any order on the application.

Tey faces six charges of having corruptly obtained gifts and sex from Ms Ko between May and July 2010.