In a dramatic exchange in Parliament on Tuesday, Environment and Water Resources Minister Vivian Balakrishnan accused Workers' Party MPs Sylvia Lim and Pritam Singh of making "false and untruthful" statements on the recent hawker centre cleaning dispute.

Providing a full account of what he described as a "sorry episode", Dr Balakrishnan said the witnesses and the evidence clearly led to the conclusion that a property manager of the WP-run town council in Aljunied GRC had asked hawkers at two Bedok hawker centres to pay extra for annual cleaning.

This, despite the standard practice for at least the past decade that the town council should have foot the bill. The request was made, furthermore, on at least three separate occasions, he added.

Ms Lim maintained that the WP had not been untruthful.

But, Dr Balakrishnan countered that in the face of "incontrovertible evidence", repeated denials by Ms Lim and Mr Singh that the property manager had made any such request were "very, very troubling".

Suggesting that this amounted to a cover-up, he said the crux of the issue was "clean politics", not the "cleanliness of the (hawker centre) ceiling".

During the exchange, which lasted 36 minutes, Ms Lim categorically denied the allegations of falsehood and reiterated that the issue was a misunderstanding rooted in a misleading email from the National Environment Agency, and confusion over whether the cleaning being discussed were annual or quarterly ones.

Ms Lim, the chairman of WP and the town council which the hawker centres in question come under, did not deny that they were responsible for cleaning the ceilings of the hawker centre once a year.

But, she said there was no law stating which time of the year this had to happen.

Midway through the exchange, Dr Balakrishnan distributed to MPs a dossier of evidence, with email and meeting minutes to back up his case that Ms Lim had been untruthful. Ms Lim denied that the evidence proved the allegation.

In his conclusion, Dr Balakrishnan turned to WP chief Low Thia Khiang and said: "I appeal to you. Go back, do a thorough investigation of what's gone on and what's wrong in your town council and put it right. I have confidence that you will do so, Mr Low."