Sex slaves investigation: Girls hidden in plain sight

• Sex slaves on your doorstep

• Escort websites important to police inquiry

• It feels dirty and wrong - a business transaction

The time and address had been confirmed via text less than 24 hours earlier.

A text simply provided the post code and street address after my request for a 15-minute in-call.

A stone's throw from the bustling market square, it was not the sort of secluded and discreet location I had expected.

I wondered if the dozens of people walking by or waiting for a bus were aware that an organised sex trade was in full swing under their nose.

Approaching the green doorway in Bridge Street I pressed a button on a seemingly lifeless intercom. Unsurprisingly there was no reaction so I telephoned the number listed on the escorting website.

Within seconds the voice of an Eastern European girl answered. The door opened and she instructed I walk up the stairway to the 'last door' on the top floor.

I began to scale several flights of steps up to the highest level of the building – at that point I was oblivious to the fact my movements were being monitored by two sentries patrolling outside of the building.

Upon reaching the top floor I was presented with three doors, but before I contemplated knocking any of them the one to the left opened.

I breathed an inward sigh of relief at the sight of the same girl who had appeared on the online profile.

Stepping into an unremarkable looking corridor it was notable only for its lack of features.

The walls were painted cream, while the floor was carpeted in a similar shade.

I counted up to three doors on each side, while the hall led ahead of me and round a corner to the right.

In every aspect it resembled a typical student digs but somehow I suspected there was not much studying going on behind each of those doors.

Avoiding eye contact and remaining silent my escort led me into the second room on the left.

A double bed topped with a leopard-print cover accounted for 80 per cent of the floorspace in what appeared to be a room fit for only one purpose.

Accessories from hair straighteners to shoes lay piled up at the foot of the bed.

A sizeable window with a net curtain was the only feature to break up the bland but cleanly painted walls.

In our first verbal exchange the young woman, speaking in broken English, asked 'how long you wanna stay?'

Having already requested 15 minutes over text I suspected that perhaps the recipient of those messages was a third party managing this particular girl – and maybe many more.

Upon handing over the necessary amount of cash she told me to take off my clothes saying 'I will be back in a minute'.

Feeling a little in over my head I took off my top. Within seconds of her return she swiftly undressed instructing me to take off my trousers.

I sheepishly obliged, remaining in my boxer shorts, but stated I was only there for a back massage.

It prompted a puzzled expression from the sex worker who replied 'I don't understand?'

At that point I fumbled through a semi-rehearsed cover story that I had never done this sort of thing before and was too nervous to do anything intimate on this occasion.

Proceeding to lie on her bed face down she began to massage my back to the tinny soundtrack of a techno-heavy song coming from a poor quality sound system.

But before long she reached for contraception clearly assuming I was ultimately there to have sex.

Repeating my excuses I declined once more provoking a reaction of sheer bemusement.

Nevertheless with my intentions now made abundantly clear I began to ask her some questions, partly in a bid to divert any suspicions.

Originally from Bucharest, Romania, she claimed to have not been in England very long whilst working as an escort for a year in total.

When asked why she came to Walsall she replied 'I come with friend, he get this house' while her frank response to whether she preferred it to her homeland was 'It is better money'.

Following further enquiries she said she would have around 'three, four or five' customers on a typical weekday like this one while weekends were much busier.

Asked how long she intended to work in the sex trade she responded 'When I leave I don't ever want to work again'.

A quarter of an hour had soon elapsed. I got dressed and left saying thank you to which she replied 'you're welcome'.

As I exited the door at the end of the corridor and made my way to the top of the stairwell I paused to make way for a man coming towards me.

In a distinctly Eastern European accent he muttered 'thanks' as I made my way back out onto the street.

Meanwhile, another undercover reporter was monitoring the situation outside.

He tells his story: "Like anything of value, it needs protection.

The 22-year-old escort was hosting my colleague, letting him inside her compact space and putting herself in potential danger.

I watched my co-worker nervously walk up to the front wooden door to the high apartment block in Walsall. Although in the town centre, it was discreet.

He was eventually let in. The door unlocked and in he walked, gone. I believed it was the last activity I'd see until the 15 minutes had subsided – but I was wrong.

Within minutes two men appeared outside the address.

One followed my colleague inside the block using the key code to the building, the other smoked a cigarette and walked in the bookies opposite.

I followed him inside.

He checked his phone, made a bet on the horses and then stood around inside, obviously waiting.

He made a couple more bets, played on his phone.

Then suddenly he walked out of the bookies, over to the apartment block and through the door.

It turned out my colleague was just leaving, he passed the man on the stairs. Coincidence? Or was this the escort's protection?"