I had a really happy childhood in Liverpool in the 1960s. Even though it must have been hard financially, Mum and Dad never showed me and my siblings that side of things. I’m 59 now and have my own children. One of my three daughters, Jessica, passed away almost three years ago and my marriage broke down. That was horrendous for the children and I’ll carry it for ever, because it was me who walked away. One of my daughters, Rebecca, is 34 and lives with me now.

It was from this perspective that I began to think about who has the right to steal a happy childhood from a child. I have never experienced sexual abuse, but when I came across a film made by a paedophile-hunter group on the internet, I identified with what motivated them. I liked the way Catching Online Predators (COP) went about their business: strictly within the law, rather than acting like out-of-control vigilantes.

They are decent, ordinary men and women with regular jobs. I followed them on Facebook and in March last year sent a message to the guy who ran it. I had a phone interview and they made sure I had no criminal record (as a nurse, I am DBS-checked annually). The next thing I knew I had agreed to join a “sting”. Rebecca was dubious about me getting involved but, as she learned more, she became interested. She agreed to be a decoy and set up a Facebook account as an underage girl. Within minutes, she was inundated with friend requests from older men (it’s the men who have to make first contact to avoid claims of entrapment). Some of the things that were said, and the images sent to her, were just awful. Take my word for it: it’s not just a few weird men on social media, it’s an epidemic.

A sting takes place when the predator has either arranged to meet the decoy or his online behaviour has given serious cause for concern. There will be a discussion about whether it will be a sting in a public place, or a knock on the door. A risk assessment is made and a plan devised by whichever group is taking the lead.

Thomas Jean De-Castle-Lynne, who was 46, stood out because of the way he spoke to the decoys. He was aggressive. On this occasion, last April, he had arranged to meet someone he thought was a 14-year-old girl at Stevenage train station. As I travelled down with another member of the team, I was apprehensive. The adrenalin was pumping. I was part of a security team of seven, rather than the usual three or four. He arrived and the team identified him from his Facebook photo and stopped him in the ticket hall. We said we were performing a section 24 citizen’s arrest – the law that allows store detectives to hold suspects until the police arrive.

Once he realised he wasn’t going to be able to run away, he started violently lashing out, so we restrained him. I realised my finger was trapped in his mouth. The pain was excruciating. I was trying breakaway techniques I’d learned at work, but he would not let go. When he finally released my finger, it was flapping in the air with blood pouring out. As a nurse, I was thinking: “Has he got HIV?” I was also thinking about my daughter, who was watching on Facebook with other COP page followers (there are more than 90,000).

We remain convinced that if he had met a real child, she would never have survived. He was arrested at the scene and I was rushed to theatre at the Lister hospital in Stevenage, where they tried – but failed – to reattach the little finger on my left hand. The bite took a third of it off and they had to amputate the rest. I gave evidence against De-Castle-Lynne in court: it was important for me to look him in the eye to say, “I’m not scared of you.” He got 10 years [for attempting to meet a child under 16 following grooming, causing grievous bodily harm with intent and common assault].

I’ve since been diagnosed with post-traumatic stress disorder. I’ve not been on any stings since, and Rebecca is no longer a decoy, but we’ve no regrets. I may have lost a finger, but a family could have lost a child.

As told to Bill Borrows

In the UK, Childline can be contacted on 0800 1111, or by confidential email via its website.

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