'I knew that I had had sex, but I can't remember a thing about it'

Sarah remembers very little about the rapes. The drug she unwittingly drank gave her tunnel vision, blurred her sight and eventually wiped out her memory for two crucial blocks of time.

It was the intense bruising round her waist and two flashbacks that led her to one awful conclusion: her boyfriend Richard had deliberately spiked her drink at his firm's Christmas party at an Oxfordshire hotel two years ago.

Pliable and disinhibited by the drugs, she was twice guided upstairs to a hotel bedroom and, she believes, raped each time. Sarah believes she "lost" eight hours that night. "I knew that I had had sex, but I can't remember having it," she said.

Her experience, say drug-rape experts, is typical. "I can remember feeling disassociated but not aware that I was drunk. It's not like that... It's like you're in a void," she recalled.

"I got horrific tunnel vision. The bar was very badly lit and it looked pitch black to me. I got colour distortion and people were like in black and white.

"I was in a dream state for the next few days. I pretty much knew the next day that something sinister had happened to me, but it wasn't until the Sunday that I thought: 'I know that my drink was spiked.'"

As the weeks passed, her suspicions rested on the vivid bruises round her waist; strong feelings of having had sex without her consent; remarks made by her boyfriend about her "bad" behaviour at the party; and her uncharacteristic, unexplained loss of memory.

The whole affair was a profound shock. Sarah, in her late 40s at the time, was a divorcee living with three daughters in northern England, working as a secretary. She began taking anti-depressants. Then she received a chilling call from a friend.

Her friend said Sarah should take an Aids test – her ex-boyfriend had been seen in some notorious sex clubs. Sarah began her own investigation, talking to his colleagues and hotel staff. "I was suffering quite badly. You don't trust yourself, and the confusion with losing your memory is very, very stressful. So I kept seeking answers."

Witnesses said Richard and his boss had twice taken her upstairs, and Richard later made up stories about her being unbalanced to other partygoers. She challenged him to explain what had really happened, but his evasive answers contradicted what witnesses had said.

Still convinced that her ex-boyfriend had attacked her, she confronted him again. This time he physically assaulted her, again producing tell-tale bruises and friction burns.

It was not until April – four months after the party – that Sarah felt confident enough that she had grounds to make an official complaint. Her first complaint was taken down and dropped, for lack of evidence.

Some weeks later, a detective took her allegations seriously and Richard was interviewed. Again, the case was dropped. There was no evidence and no witnesses. "The CID officer said he had no doubt something untoward had happened, but without any evidence, unless I got a confession, he would get away."

Sarah is now a victim counsellor for the Drug Rape Trust, and has spoken to dozens of complainants. Many have the same story: losing time, a sense of deep confusion and self-doubt, and disbelief from the police.

"They don't know whether to believe themselves, and that's the really distressing thing about it," she said. "It's very, very distressing to know you've been raped and had no control."

The names in this article have been changed.