A British businessman and his partner were arrested in Hong Kong yesterday after their 15-year-old daughter fell to her death from their £7.5million apartment.

Nick Cousins, 57, and Grace Garcia Cousins, 53, were held over alleged 'ill treatment' of their child after it emerged that her birth, and that of her 14-year-old sister, were never registered and they did not attend school.

The couple were also being questioned by police over claims that Filipino Mrs Cousins had overstayed her visa.

The 15-year-old daughter of Briton Nick Cousins (left) and his partner Grace (right) fell to her death from their multi-million pound flat in Hong Kong

Police said the girl, Blanca Cousins (right) had been unhappy and a police source said she locked herself in a bathroom before falling to her death as her parents tried to unlock the door

Police sources say Blanca (pictured) was watching television in the apartment's master bedroom while her parents watched TV in the living room shortly before the tragedy

A police spokeswoman said a security guard found Blanca lying on the ground at the foot of the apartment block shortly after 1.46am

Tragedy: Blanca fell to her death in an apparent suicide early on Tuesday morning after locking herself in a bathroom of the apartment in Hong Kong's exclusive 3 Repulse Bay Road (pictured)

Mr Cousins, originally from Thurrock, Essex, is managing director of the Hong Kong arm of international insurance broking firm Jardine Lloyd Thompson, and has worked for the firm in Asia for more than 20 years.

There were claims last night that Mrs Cousins had originally moved to Hong Kong from the Philippines in the 1990s and worked as a domestic helper before becoming the partner of Mr Cousins. It is unclear whether they had married, although she uses his surname.

It is believed the couple had been watching television in the family's home on the 21st floor of one of Hong Kong's most luxurious apartment buildings before Blanca's mother found her daughter was locked in a bathroom shortly before 2am.

Blanca fell to her death from a window just before dawn. Paramedics declared her dead at the foot of the building in Repulse Bay.

Police sources claimed while no suicide note had been found they were aware the girl had been 'unhappy' in recent weeks.

The girl's father has been named as Nick Cousins (pictured) the managing director of insurance broker Jardine Lloyd Thompson's Hong Kong office

Blanca – who was known as Blancs – was due to celebrate her 16th birthday in July.

She was a member of the Hong Kong Pony Club and was understood to have been educated at a private tuition centre along with her younger sister.

School attendance is mandatory in Hong Kong, but a more relaxed approach is taken with expatriate residents and some 'home school' their children without official permission. However, not having their births registered meant the girls would not have been able to get either compulsory identity cards or passports to pass through the territory's strictly controlled borders, which suggests they spent their entire lives in Hong Kong.

Last night, one expat who knows Mr Cousins described the family as 'down to earth and decent'. He added: 'He isn't a Hooray Henry at all, like so many of the expats in top jobs in Hong Kong. He's more of an Essex-boy type who worked his way up the corporate ladder and is just very bright and very good at what he does.'

Both of the Cousins girls appeared to have a wide circle of friends among the city's well-to-do expatriate community. Carla Cousins – Blanca's younger sister – recently posted pictures on Facebook revealing that her father had a company box at last month's Hong Kong Sevens rugby tournament and invited friends to join her at the event.

The 21-storey apartment block is one of the city's most prestigious addresses, with four-bedroom apartments selling for £7.5million each while they rent for £8,000 a month.

The 21-storey apartment is one of the wealthy city's most prestigious addresses with luxury four-bedroom apartments selling for prices in the region of £7.5million

A police source last night said: 'Initial investigations showed there were no suspicious circumstances and [Blanca] was suspected to have fallen from a height.

'We arrested a 53-year-old Filipino female for overstaying and a 58-year-old British male for aiding and abetting an overstayer.

I did see them out and about as a family in Repulse Bay at weekends. No one suspected they weren't married

'Both have also been arrested for suspected ill treatment of the girl. Our investigations indicate the girl was unhappy with her life.'

Last night a spokesman for the Jardine Lloyd Thompson Group said: 'We can confirm that our colleague Nick Cousins, the managing director of our Hong Kong office, has suffered the loss of his eldest daughter in tragic circumstances. We are giving Nick our full support through this difficult time and he will be on compassionate leave until further notice.

'We are aware that the authorities are investigating a number of matters that have come to light in the wake of this tragic event. As these are private matters, it would not be appropriate for us to comment further.

'Our thoughts are with Nick and his family.'

Mrs Cousins was last night still being questioned over allegedly overstaying her original visa while Mr Cousins was released on bail.