A kitchen porter has been found guilty of grooming and wounding with intent after biting the tip off a paedophile hunter’s finger at Stevenage railway station while on his way to have sex with what he thought was a 14-year-old girl.

The trial at St Albans Crown Court heard that Thomas De-Castle-Lynne, of Parsons Green in London, was caught in a sting by a group called Catching Online Predators.

The 46-year-old arrived at Stevenage station on April 8 thinking he was going to meet a 14-year-old girl for sex in the woods, but was then surrounded by the vigilantes.

In a struggle he ended up on the ground with one of the group, Stephen Little.

Mr Little told the jury: “All I can remember is that, as we restrained him, we took him to the floor. He clamped onto my finger with his teeth. I remember excruciating pain.

“I called for him to let go. I noticed blood coming out of his mouth – it was my blood and he just wouldn’t let go.

“He was lying on the floor and there were two others with me. I had my knee on his right shoulder. I was screaming at him to let go of my finger.”

Asked by Angus Roberston, prosecuting, how long his finger was in De-Castle-Lynne’s mouth, he replied: “It felt like a lifetime, but was probably two to three minutes.”

After his finger was released, he said: “I noticed immediately the whole finger appeared white – there was no blood in it.”

Mr Little was taken to hospital – the wound did not heal and the tip of his left little finger was amputated.

The jury of eight men and four women was told by the prosecutor Mr Robertson: “In March this year the group set up a decoy Facebook account in the fictitious name of Maddie Parker.

“The defendant made contact and in conversations he made sexual references and sexual suggestions.

“He arranged a meeting. It was clear from his tone that his intention was for sexual activity to take place.”

When De-Castle-Lynne asked how old the girl was, she told him she was 14.

He asked: “Are you a virgin?” She replied: “What do you mean?” He said: “Have you had sex?” She replied: “No”.

When he asked if she would date an older man, she told him she had never had a boyfriend.

The court heard that De-Castle-Lynne asked her for her breast size and the colour of her nipples, before saying: “I want to have sex with you babe.”

When he thought she was travelling on the train to Stevenage, he told her to take off her bra and panties and put them in a bag.

The prosecutor said De-Castle-Lynne was also having Facebook conversations with three other “decoy” girls set up by Catching Online Predators. In a conversation with a fake 13-year-old called Georgie, he asked for photos and said they would meet in woods for sex.

He asked a 14-year-old called Leah for pictures of her breasts and vagina, and arranged to meet a 13-year-old called Lara on April 9 after asking her to remove her underwear.

In the witness box, De-Castle-Lynne was asked if he had an interest in young teenage girls. He replied: “Hell no – they annoy me.”

His barrister Daniel O’Malley asked: “If you knew it was not a real person why get involved?” He replied: “I just wanted to p*** the person off. To wind them up and tease them and call them out.”

The jury delivered their verdict on Monday, finding De-Castle-Lynne guilty of attempting to meet a child under 16 following grooming, causing grievous bodily harm with intent and common assault. He was cleared of assault by beating.

During the trial, he changed his plea to guilty to causing racially-aggravated harm or distress after telling one of the hunters to shut up using a racial slur.

He was remanded in custody by Judge Michael Kay QC to be sentenced on November 29.