A convicted extremist who was a member of the so-called "Muslim Patrol" has apologised to his victims and told Sky News he has been reformed.
The 21-year-old was actively involved in targeting couples holding hands, people drinking alcohol, and women who the group deemed to be dressed "inappropriately".
Horner was jailed for 17 months in December 2013 after pleading guilty to charges of assault and of using threatening words and behaviour.
Now on licence from prison, he says he thinks about the harm he caused "on a day-to-day basis" and now rejects extremism.
"I apologise to the individuals that I did harass and attack. Somebody who makes mistakes never recognises they're making a mistake until they analyse what they've done after they've done it."
Horner told Sky News how he felt he needed to physically implement his religion rather than practise it on a spiritual level - propagating it on others.
"Now I've moved away from that and I've studied my faith correctly and I understand that these are the type of actions that are completely incorrect."
Horner also admitted that his actions could have caused Islamophobia - and for the past year, has been working with an agency which claims to have reformed 20 extremists in the past six years.
Usman Raja, who runs the Unity Initiative, says the organisation's goal is to tackle the "mistranslation" of Islam by using the teachings of respected scholars.
He explained: "You're dealing with ideas that have been embedded for years. You're not changing their favourite colour – you're going in and you're dealing with a world view.
"You're trying to take them from a place where they view themselves as part of a group and bring them into the rest of humanity, into the rest of the world, so they see themselves as not separate from that."
Horner describes his radicalised views before he was jailed as a "clash of society" when he had an "us and them" way of thinking.
After working with Usman, he says he still has "principles as a Muslim" of not drinking and smoking - but adds he knows it is wrong to force them on other people.