This is the moment a British landlord opened his flat door to find two prostitutes, realising his property was being used as a brothel by a Brazilian organised gang.

Property developer Craig Shepheard had let out his modern apartment in St Albans, Hertfordshire, and thought the tenant was someone working as a courier.

But after complaints from neighbours about men visiting late at night, he investigated and realised his home was being used by a gang who operate pop-up brothels.

Now, a new BBC Panorama investigation called 'There's a Gangster in My Flat' has uncovered how gangs are using homes obtained through reputable letting firms.

The crooks use fake identity documents and references to pass tenancy checks before obtaining keys to properties from which they can operate criminal networks.

They are also often able to avoid prosecution despite evidence of criminal activity, meaning the onus falls on landlords to pursue possession through civil courts action.

Explaining the situation four years ago, Mr Shepheard told investigative journalist Hazel Martin: 'The vast majority of my tenants are absolutely lovely.

'I provide good quality, really nice places to live. I was using a professional lettings agency, and they got this chap in who passed all of the tenancy checks.'

Property developer Craig Shepheard filmed a sex worker in his flat in St Albans, Hertfordshire

Mr Shepheard filmed one of the women calling the man who had organised the room for her

The owner realised that his flat was being used as a brothel and reported the situation to police

The St Albans home was being used by a Brazilian organised gang operating pop-up brothels

While the new tenant seemed fine for the first few months, the rental payments then stopped and Mr Shepheard began receiving complaints from neighbours.

He said they told him: 'We've got issues with your tenant. We think they might be smoking cannabis. They've blacked out both sets of the windows, which is really weird.'

Things escalated when he started to receive reports of men visiting the flat at night – so, when the tenant claimed the washing machine had broken, he went to investigate.

Mr Shepheard found what he described as 'sexual paraphernalia' in a cupboard and instantly suspected his flat was being used as a brothel – reporting this to police.

Officers began investigating but said more evidence was required for a search warrant, so he went back to the property and started filming men entering the flat.

One week later he told the tenant he needed to do an inspection, adding: 'I literally opened the door and there was a double bed there with a blonde, naked lady covered in tattoos fast asleep.

'We then came through into the second bedroom, and there was another double bed with a man and a lady asleep. She woke up and screamed because there was a strange bloke standing in the doorway.

'The first lady woke up and came out with a dressing gown on and that's when I started having a conversation with them.'

Property developer Craig Shepheard thought the tenant was someone working as a courier

There were complaints from neighbours about men visiting the flat in St Albans late at night

Investigative journalist Hazel Martin looked at the situation for the BBC's Panorama programme

Mr Shepheard identified himself as the landlord and then secretly filmed his conversation with one of the women, who called the person she was paying rent to.

He later translated what the woman said as: 'Could you please call and speak to the man because he's being a nuisance here. We have a client here in the room, please.'

Detectives then revealed to him the women were part of an organised prostitution ring run by a network in Brazil, who operated pop-up brothels which saw the women moved around flats across England.

Mr Shepheard said: 'They admitted they were sex workers, paying £400 each per week for the availability of that room.'

He said they used a small local letting agency who met the tenant and saw proof of ID – but it was a faked passport, which immigration officials later described as 'one of the best forgeries they had ever seen'.

The tenant's real identity was never found and the two sex workers vanished.

Housing law meant the tenant could keep the flat despite running a brothel being illegal, but Mr Shepheard's solicitor eventually tracked him down and persuaded him to give up the flat.

Mr Shepheard said: 'There was four and a half months of unpaid rent plus a £4,500 repair bill just to get the property back onto the rental market.'

Confirming he was now planning to sell the property, he added: 'I had done everything right and made sure the tenant had been checked 'officially' through a professional lettings agent.

'After all the shenanigans about getting the police involved to carry out a search warrant and finally getting the tenant evicted and getting the property decorated, it's crazy, it's just too much hassle for not enough gain.'

'Panorama - There's A Gangster In My Flat' is now streaming on BBC iPlayer