LONDON  - Billionaire Hans Kristian Rausing, the heir to the Tetra Pak fortune, has been arrested on suspicion of murdering his US-born wife Eva but is not yet fit to be questioned, British police said. Police discovered the body of Eva Rausing at the couple's home in London's wealthy Belgravia district after they detained her husband over drugs charges earlier this week. At the opening of an inquest into her death on Friday, Scotland Yard detective Sharon Marman said Hans Kristian Rausing, 49, was currently under medical supervision and detectives have been unable to interview him.

"He has been arrested on suspicion of her murder and we await notification of when he will be fit to be interviewed," Marman said.

Marman said police had stopped Hans Kristian Rausing's car in south London because they suspected he was driving under the influence of drugs or alcohol, and they discovered a small amount of drugs.

"Authority was granted to search the home address... and during the course of that search officers discovered the apparently lifeless body of a female in one of the bedrooms," she said.

A post-mortem examination proved inconclusive and further test results are awaited, Marman said.

She did not comment on reports that Eva Rausing's body had lain in the house for several days before it was discovered.

Inquests are opened whenever there is a sudden or unexplained death in Britain.

The Rausing family, headed by Rausing's father Hans, is the 12th richest in Britain, worth £4.3 billion ($6.7 billion, 5.4 billion euros), according to The Sunday Times newspaper's Rich List 2012.

Slim, blonde and glamorous, Eva was the daughter of Tom Kemeny, a wealthy US Pepsi executive whose family lives on an exclusive island off the South Carolina coast.

Eva and Hans Kristian Rausing were active philanthropists and enjoyed an affluent lifestyle, spending much of their time in their 11-bedroom mansion in Barbados - but had well-publicised problems with drugs.

The couple, who have four teenage children, first met at a US addiction clinic and were charged in 2008 after Eva tried to take crack cocaine and heroin into a function at the US embassy in London.

Although they were initially charged with drugs offences, prosecutors subsequently decided to drop the charges and instead give them a conditional police caution.

Rausing's father Hans, 86, moved to England in the 1980s in order to avoid Sweden's high tax rates and lives with his wife Marit on a vast estate in Sussex, southeast England.

He developed the Tetra Pak business, which had been founded by his own father in 1944, into a multi-billion dollar operation that revolutionised the packaging of food and drink.

He sold his 50 percent stake in the company to his late brother, Gad, in 1995.