Hans Kristian Rausing, Tetra Pak cartons billionaire and one of Britain’s richest men, was being questioned last night about the mysterious death of his wife Eva.

Hours after Hans Kristian Rausing, 49, was arrested on suspicion of possessing drugs, his wife Eva’s body was found in a bedroom at their London home.

Hans Kristian Rausing, a father-of-four, an heir to the $7.2 billion Tetra Pak drinks carton fortune, was being questioned in connection with what Scotland Yard called an “unexplained death”.

Last night police said Hans Kristian Rausing remained under arrest but had been taken to hospital for medical treatment.

Officials refused to discuss why but the news prompted speculation that he had suffered some kind of breakdown. Earlier, security staff was called in to help download CCTV cameras from the Chelsea mansion and surrounding area.

Hans Kristian Rausing was being questioned last night about the mysterious death of his wife Eva

A post mortem examination was carried out yesterday afternoon on 48-year-old Eva Rausing, but failed to find the cause of death. Further toxicology tests will take place to determine whether drugs or alcohol were responsible.

Her husband of almost 20 years was arrested on suspicion of driving erratically in South London at lunchtime on Monday and was found to be carrying Class A drugs. Officers searched his home to see if more illicit substances were there, and found his wife’s body.

Eva Rausing

Specialist police teams carried out tests throughout yesterday at the six-storey house in Cadogan Place.

Details of their son’s arrest and daughter-in-law’s death were broken to 86-year-old Hans Rausing and his wife Marit at their 900-acre East Sussex estate. They issued a statement saying they were “deeply shocked and saddened”.

Eva Rausing’s father Tom Kemeny is a former Pepsi executive who owns an island off South Carolina and a property in Barbados with his wife Nancy. The couple also has a $16million property near their late daughter’s home in Cadogan Place.

They said of their daughter: “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.”

Eva Rausing was a co-patron with the Duchess of Cambridge of the drug charity Action on Addiction. Officials said they were “devastated” by the tragedy.

Within hours of the discovery of the body, police seized security CCTV footage from inside and outside the property focusing on Cadogan Place and a mews at the rear.

Yesterday morning a detective showed a security expert out through a back door of the house and walked up and down the mews lane, working out which CCTV cameras had a view of the Rausings’ back door. An hour later, the security technician removed a CCTV hard disk drive from inside the house.

Neighbors include Philip Havers QC – whose father Michael was Attorney General and then Lord Chancellor before becoming Baron Havers. His brother is the actor Nigel Havers.

In recent weeks, Hans Kristian and Eva Rausing had seen out walking in the area. He often wore a baseball cap while clutching a pack of rolling tobacco. His wife wore cut-off trousers and open-toed sandals.

In addition to their London property, the couple had an 11-bedroom beachside mansion in Barbados and an apartment on The World, a cruise ship for passengers who need to be off shore for tax-avoidance purposes.