Police outside a house in Cadogan Place, Belgravia, where Eva Rausing, a member of the family behind the Tetra-Pak drinks carton empire and one of the richest women in Britain, was found dead. Photo: Leanne Rinne/PA Wire

More tests are to be carried out to establish how Eva Rausing, one of Britain’s richest women, died.

Police investigating the mysterious death are thought to have arrested Hans Kristian Rausing, the heir to the Tetra Pak drinks carton empire, after the body of his wife was found at the couple’s home in Cadogan Place, Belgravia.

Mr Rausing, who stands to inherit a billion-pound fortune from his father’s business, is believed to have been taken into custody at a south London police station - but later moved to a “medical facility” where he is receiving attention, police said.

Scotland Yard would not confirm the name of the suspect, but said a 49-year-old man was arrested in south London on Monday morning on suspicion of possession of drugs.

Then, later that afternoon, officers conducted a search at an address in Cadogan Place where they discovered Mrs Rausing’s body.

The man was then further arrested in connection with the mother-of-four’s death. His bail has been suspended while he receives ongoing medical treatment, the force said.

Police are treating the death of Mrs Rausing as “unexplained” and a post-mortem examination yesterday failed to establish a formal cause of death.

Investigators said they are awaiting the results of further tests in the hope they will shed some light on the death riddle.

Grieving relatives of the married couple, whose past drug problems have been widely reported, last night revealed their sorrow over the death.

A statement from the family of Mrs Rausing, whose maiden name was Kemeny, said: “Tom and Nancy Kemeny along with all of their family are deeply saddened by the death of their beloved daughter, Eva Louise Rausing.

“Eva was a devoted wife for 20 years and mother of four much-loved and wonderful children.

“During her short lifetime she made a huge philanthropic impact, supporting a large number of charitable causes, not only financially, but using her own personal experiences.

“She bravely fought her health issues for many years. The family is devastated at her death and asks to be given privacy at this difficult time.”

The Rausing family said they were “deeply shocked and saddened to hear of the tragic death of their daughter-in-law” and also asked for their privacy to be respected.

Mr Rausing stands to inherit the £5.4 billion business enterprise built by his Swedish father, also named Hans.

In 2008 Mr Rausing and his wife were in trouble with the police over drugs but the prosecution was formally discontinued.

Mr Rausing, then 45, was charged with drugs offences after police found crack cocaine, cocaine and heroin during a search of his home.

After lengthy discussions between his legal team and prosecutors, he accepted a conditional police caution instead.

Neither Mr Rausing nor his wife, who also faced drugs charges, was present at City of Westminster Magistrates’ Court that August to hear that the prosecution had ended.

The couple had been arrested in April of that year after Mrs Rausing was caught with drugs as she tried to enter the US Embassy in London.

Court documents revealed Mrs Rausing, then 44, was carrying about 10g of crack cocaine, 2.5g of heroin and 2.35g of diethylpropion, a banned stimulant and appetite suppressant.

A further drugs stash, 220mg of diazepam, used to treat anxiety, was also found in her Renault Clio car.

The couple’s £5 million Georgian five-storey town house in Cadogan Place was subsequently searched.

Officers found 0.2oz (5.63g) of crack cocaine, 0.1oz (2.9g) of heroin and almost 1.8oz (52g) of cocaine.

The conditional cautions, administered by a senior local officer, meant the couple admitted possessing the drugs.

Mr Rausing’s parents and siblings said then they were supporting the couple as they fought to overcome drug addiction.