Justin Davies, a wealthy 41-year-old from Fulham, west London, admitted two charges of drugging his wife Sally, 36, with Flunitrazepam, the scientific name of the drug.

Rohypnol: Prescribed for insomnia

The Old Bailey was told by his counsel Patrick Gibbs that there was no sexual motive involved in the crime.

He simply wanted to save his floundering marriage. The couple have since divorced.

The court heard that he discovered the prescription-only drug helped him sleep on a transatlantic flights. He then decided to slip it into his wife's glass of wine one evening.

The following morning she woke up feeling "totally disorientated".

Her husband told her: "We had a really nice chat last night and you told me you did not want a divorce."

That evening, Mr Davies spiked his wife's drink again. She became suspicious when Davies, who was normally untidy, made an effort to clear away bottles of wine.

She noticed one bottle was cloudier than another and alerted the police.

The wine and a glass were analysed and found to contain Flunitrazepam.

'Misguided intentions'

She has since forgiven her ex-husband.

Sentencing, Judge Geoffrey Grigson told Davies: "Ordinarily for an offence of this nature, I would not hesitate to pass an immediate custodial sentence.

"Had your motive been sexual, you would have been on your way to prison."

He added: "Your intention, however misguided, was to save your marriage for the sake of your son.

"Perhaps most important is what has happened since. The attitude of your ex-wife in particular towards the future of your son.

He also praised Mrs Davies as "a lady of great strength and understanding".

Outside court, Detective Inspector Robin Cross, told reporters that claims the drug could not be detected were a myth.

"It is a misconception that it cannot be detected. The danger is that victims do not usually realise something is wrong," he said.

Rohypnol is odourless and tasteless when put into drinks. But the manufacturer, Hoffman-Roche, has now introduced a chemical which turns drinks blue when it comes into contact with the pills.

It has been used to drug rape victims who suffer loss of memory, lose inhibitions and may not realise they have been drugged.