A 39-year-old Southwark man was convicted at the Inner London Crown Court last week of administering a substance with intent to commit a sexual offence.
Businessman Rohail Spall pleaded not guilty at the trial which started on 27 November.
The court heard that on 13 June 2006 the victim met Spall for a pre-arranged dinner date. She had met him previously whilst in the company of her friend in a bar in Canary Wharf where he engaged them both in conversation and exchanged phone numbers.
He gave her the impression he was a high-powered, respectable businessman working in the city.
After the victim had finished work they had a few drinks in a bar in Canary Wharf and then went to a restaurant in Borough, SE1, in Spall's chauffeur driven Mercedes.
In the car, Spall kept trying to kiss the victim which she tried to rebuff by moving to sit in the opposite corner of the car.
At the restaurant, the victim immediately went to the toilet. Whilst she was away Spall approached the head waiter and said that the victim was his girlfriend and that he wanted to have sex with her so asked if he could keep her glass refilled.
The suspect whispered to the waiter again out of hearing of the victim saying that even if the victim didn't order any more drinks he should keep bringing her more. The waiter said that Spall whispered to him at least three times and on one occasion said that he wanted something strong, something special as he wanted her to be knocked out.
During the meal Spall kept telling the victim to have red wine but she couldn't understand why as they were having fish.
Whilst eating Spall kept telling the victim to stay the night at his place and when she disagreed he persisted in trying to persuade her.
The waiter became suspicious of the man due to the comments made to him. Whilst he did so he noticed the man dropping a tablet into the victim's drink when she went to the toilet. The waiter spoke to the victim as she came out of the toilet and told her what he had seen. The manager was alerted and the police called.
When police arrived Spall was searched and a blister pack of tablets was found in his pocket with one tablet left. The name on the blister was XANAX, a drug with similar effects to Rohypnol.
Spall was arrested and taken to Walworth Police Station where he made no reply to the caution.
The tablet and the contents of the victim's drink were sent to a Forensic Science Service laboratory for analysis where it was confirmed that the drink contained the drug.
"Fortunately this type of incident is rare however this case highlights just how dangerous men like Spall are," said DS Brian Willis, speaking after the conviction.
"Thankfully due to the astute actions of the waiter Spall's offence was spotted and he was caught. The MPS views this type of crime very seriously and will always seek to bring offenders before a court. I would urge women to remain vigilant and to be alert particularly at this time of year."
Spall is due to be sentenced on 5 January 2007.