IT was after repeated knocks on a door went unanswered that HDB officers were about to give up. The window shutters and doors were firmly shut, yet bright lights and faint noises from within the flat was betraying the tenant's presence.

Just as the HDB team was about to walk away, the door opened and a young girl of 15 emerged. HDB officers started quizzing her: Who are you, what's your name, how long have you lived here, who do you live with.

She looked terrified, but she answered all the questions behind the locked grilles separating her from us: I've been here for only a week, I'm staying with a female "parent's friend".

One HDB officer (let's call him Mr Tan) looked at me and whispered, "this flat is rented to a man born in the 1930s!"

A laptop, books and personal items litter the two-room flat, suggesting the occupant - a secondary three student from Thailand - is the sole tenant of the flat. She later revealed she paid $1,000 a month to live there. PHOTO: HDB

Caption: A 'Notice to Quit' letter is pasted on the two-room flat's door the next day, for the tenant to contact HDB and to evict the flat within one month. PHOTO: HDB

It was obvious at that moment that our inspection had uncovered a case of illegal subletting, which was recently reported to be on the rise.

This was the moment I had been waiting for, the climax of the "enforcement blitz" which we carried out at Circuit Road last week. But somehow, I had imagined a more dramatic unfolding of events, perhaps with officers loudly knocking on doors, demanding to be let in, "guns" ablazing. Illegal tenants confessing. Maybe even crying. And with lengthy interrogation techniques deployed by officers required to induce the truth.

In reality, the whole episode was more sobering than dramatic.

I realised, it was important for the HDB officers to be un-dramatic, in fact. They had to appear normal, routine even, so as to be unconfrontational, to gather the evidence and information they needed from the illegal tenants.

In the case of this girl, Mr Tan had to repeatedly assure her it was a "routine HDB inspection" and that he only had a few questions. He requested to see her IC, and it revealed she was a Secondary Three student from Thailand attending a school located nearby. After getting no answers as to who her "parent's friend" was, Mr Tan requested that the girl unlock the gates for the officers to "take a look".

The girl hesitated, unsurprisingly. There were about 10 of us on this "mission" which no doubt was intimidating.

Then she relented and unlocked the gates. Three officers entered, and promptly started taking notes and photographs with their flashing digital cameras.

At this point, the girl looked increasingly worried.

I went into the flat myself, and looked around while Mr Tan pointed out the evidence in the flat: only one bed. Young female clothing, books, and bags strewn all over the place. No sign of any man or woman living there.

It was when Mr Tan told her that he needed a statement from her, with her signature, that the girl caved in and confessed that she lied about staying there for a week. She revealed to gasps all round that she paid $1,000 a month to live at the flat - which the HDB officers told me was rented out for only $44 to the 70-year-old man.

The poor girl was obviously ignorant of the rules of the game. At one point, Mr Tan even gently asked her, "Do you know what's the HDB?"

He had to explain what the Housing Board was, and how the flat belonged to them and was rented out to Singaporeans. All the while, he kept reassuring her that she wasn't in trouble, although she looked stricken with anxiety.

Having been so compliant so far, the girl flatly refused to give Mr Tan the contact number of the "woman" who was her "parent's friend" who rented her the flat. She wouldn't say either, if the woman was an estate agent. After asking more questions, and taking down her number, Mr Tan finally thanked her and we all left, ending her traumatic experience of having 10 strangers descend into her flat.

And as we left, I realised how different the episode had been to what I'd expected.

Five months ago, I had staked out a rental block in Toa Payoh every night for a whole week, hoping to catch glimpses of foreign workers entering or departing from their illegally rented HDB flat for my story. I had heard, on several occasions, loud voices with strong foreign accents in dialogue in a brightly-lit flat, with its windows and door firmly shut. Interviews with residents had revealed then that the profile of the illegal tenant was the average foreigner worker from Malaysia, China or India, looking for a cheap place to rent. I had expected more drama from these types as HDB officers tried to catch them out on their illegal tenant status.

But what we uncovered was an unknowing foreign student, who now has to hunt for another place to live, while having to juggle her studies at the same time. I genuinely felt sorry for her.

It really brought home to me that the underlying reason why illegal subletting is on the rise in the first place is this: the shortage of cheap accommodation for the huge influx of foreigners coming into Singapore seeking a better life, whether to join the workforce or to further their studies.

True, the Singaporeans who rented out their units in the first place are primarily to blame. But it's easy to see how the tempation of getting an extra 900 bucks cash-in-hand from renting a flat out is difficult to resist, especially if that is the price that can be fetched in the current market.

While the HDB is stepping up its checks to clamp down such abuse, the sheer number of flats - some 42,000 currently - makes it difficult to ensure that none of this illegal subletting is happening.

It also suggests that perhaps the private sector is unable to provide enough supply of cheap units for such foreign workers to live. If the Government means business about reserving our very limited rental flats to the truly needy, it could do well by looking into the private rental market to ensure enough supply can be provided for the foreigners living in Singapore.

Otherwise, HDB's inspections can only solve the problem superficially. And the next tenant that moves in might just get tempted to make a quick buck again.