A detective investigating sexual assaults was devastated when he himself was raped. But he grew even more angry when police colleagues insisted on investigating the crime. Here he tells his tale anonymously

I've been a police officer for two decades and a detective, specialising in serious crime and sexual offences, for 15 years. Never once in all the time I've investigated these horrific crimes has it occurred to me that one day I would be a victim; that I would be raped – and that I would refuse to help the police investigate.

But a couple of weeks ago, I made a series of choices that led to me, a heterosexual man, waking up in a man's bed, trapped underneath him. Being raped. I'm still struggling to come to terms with how, despite my decades of professional experience, I made the choices that led to me being raped. At no point the evening before had I felt at risk. At no point did I think I was making a bad decision.

I also never anticipated using the service the police provide to rape victims. I've always been the one asking the questions. To be on the other side of the table has been a shock – if I investigated a sexual crime now, there are things I would do differently.

It's hard to accept that a couple of weeks ago everything was normal. Now everything's wrong. I had gone out with friends for a Saturday brunch. We were a small group of settled, sorted, middle-aged men, some single, some in relationships, but none of us looking to do anything other than spend some quiet leisure time together. We had a couple of beers, shared a bottle of wine over the meal, then sat around in the pub chatting and reading the papers.

As the afternoon turned into evening, people began peeling off from the group. By 9.30pm, the last of my friends headed home. On a whim, I decided to stay. I'd never been in that pub before but I felt comfortable alone there.

After a while, I got chatting to a group around the bar. I got the impression that they knew each other and they were a friendly lot. We talked about football, music, the state of the country. It was good, happy banter. It was the chat that goes on every night, in hundreds of pubs across the country when new people start getting to know each other.

As the night wore on, the accumulation of a day's steady drinking began to back up. I was never particularly drunk, I don't think, but my memory becomes increasingly misty when I try to think back.

I can't remember when I first noticed the guy who ended up assaulting me, but he stood out from the rest of the group – he was more extrovert, a bit larger than life. But he didn't do or say anything that made me feel uncomfortable – or that gave the slightest suggestion of what he would be capable of doing a few hours later.

I was still in the pub at about midnight, then the next thing I remember is being in a house with the same group of about six people. I have no recollection of leaving the pub, travelling or arriving. I've racked my brain but I don't know if we walked there, or got a bus or a cab. I do have some memories from the rest of the evening, though. I remember standing in the kitchen, talking about Christina Rossetti's poem The Convent Threshold. It developed into a conversation about poetry and what we would want read at our funerals.

Then my memory tails off again. I don't think my drink was spiked. I'll never know if I was drugged or not but I didn't have any of the after-effects you would expect. I didn't feel disorientated or woozy.

My next memory is at about six or seven the following morning. I woke up in a bed and that guy was raping me. My first thought was: "What the fuck do you think you're doing?" The second thought was fear, channelled into self-preservation: I jumped out of bed and grabbed my clothes from the floor. It didn't occur to me to arrest him. It did not even cross my mind that I was a detective. My only thought was my personal safety. He didn't try to stop me. We didn't say a word to each other.

I ran out into the street. I roughly knew the area, so I jumped on a bus heading home and started the longest journey of my life. Sitting alone on that bus was awful. My phone had died during the evening so I couldn't call anyone. I felt alone and dirty. I was very angry, disgusted, a bit scared. I needed help. I told myself what I know victims say all the time: that it was my fault for putting myself in that position. I've spent decades telling victims not to blame themselves, but now I truly understand what it means to torture yourself with "Why did I? / How could I?" thoughts. By the time I got though my front door, I had decided I didn't want to report what had happened to the police. I knew they would do a wonderful job investigating but I was thinking ahead to the trial, with me in court as the victim. I knew that anonymity at work would be impossible. Of course everyone would be sympathetic but they'd treat me differently. How could I sit there with colleagues, trying to be objective about someone else's rape if they were saying "Are you OK?" the whole time?

I knew I had to make sure I was healthy. I couldn't go to a police-run sexual assault referral centre because there was a chance I would know the staff there – the attack had happened in my town. Instead, I found the public specialist clinic. It was very good: great advice, great counselling, great follow-up service.

I called in sick to work for a few days after the attack, but I soon went back because I desperately needed some normality. I'm not gung-ho: I thought about what it would be like, listening to the stories of other victims and arresting perpetrators. How could I guarantee that I wouldn't suddenly break down? What if the man who raped me attacked someone else? How could I arrange for someone else to take over the investigation without it turning into a big deal?

My boss was also a friend, so I decided to tell him what had happened. I was clear that I didn't want to make an official report. But he called in two other officers, opened a case file and started an investigation. I was horrified. I said I wouldn't help but they kept saying they had a duty to protect one of their own.

I believe they thought they were doing the right thing, but if I'd been any other victim, my wishes would have come foremost. They perhaps felt they could put extra pressure on me because, as a copper, I didn't need the careful handling we give other victims.

I was furious but dumbfounded. The strain on me was – and still is – intense. The sexual abuse team ask me to meetings where they say the same thing, again and again: "We appreciate you don't want to substantiate this allegation but what else can you give us?" Then they say they'll come back to me in a couple of weeks to see if I've changed my mind. This relentless stress means I can't start coming to terms with what's happened to me. I want to sign a closure statement that puts all this behind me. I keep telling them that I'm not refusing to co-operate to be difficult. I tell them repeatedly that I don't want to talk about it because it was horrible and I want it to go away. I want to not think about it any more.

The worst thing was when they rang me late at night and told me they'd arrested a suspect. I have no idea who he was, and no idea what information the arrest was based on. I don't know whether they found someone based on what I told them when they were chipping away at me or whether they'd found CCTV film.

The coercion became worse. They asked if I wanted to know his name. That made me feel as sick as on the morning it happened. They obviously hoped that personalising my attacker – giving him a name and a face – would make me change my mind. Then, of course, they had to ring me back later that same evening and tell me they were going bail the guy. They had no evidence sufficient to hold him. I guess they had two goals in seeking his arrest: either I'd crack and agree to go to court, or they could take his DNA and check it on the database to see if he matched any past complaints.

My experience has led me to seriously contemplate whether I or other officers investigating similar serious sexual assaults put undue pressure on victims. Do we push victims to go through the court process? Do we do it for the right reason – because we want to fight crime – but, in doing so, not listen to what the victims are telling us? The pressure my colleagues put on me was conscious – but I think there's a risk that we do it subconsciously in other cases. That worries me deeply.

Another question I've had to ask myself is why, as a police officer, I am not doing everything I can to get my attacker off the streets. But I'm a victim first and a police officer second. I'm not the first victim to decide not to press charges, and I won't be the last. Being a cop means I know the system, and it has scared me off. I know this case would be likely to end in court and, from that point, I couldn't maintain my anonymity. I couldn't cope with the added burden of being a cop as well as a victim.

Do I have more sympathy and empathy with victims after what's happened to me? Without a doubt. Has it made me more cautious? Absolutely. But we're always wise after the event. That's not much good to me now.