Two years ago this week, my stepson came home wearing an Arabic black thawb. He walked into the sitting-room, smiled defiantly at me and at his father, and asked us how he looked. We were a little shocked, but being English of course we said he looked very nice.

Our boy had never shown any interest in religion before he found Islam at 16. We’re atheists, and we raised him to be tolerant of all faiths but wary of anyone selling easy answers. It all began after he left school. He was feeling slightly isolated, depressed and vulnerable after breaking up with his first girlfriend, so we were pleased when he began college and some new friends appeared. They were all young Muslim men. Around seven of them would pile into my stepson’s bedroom every evening and we would hear the shouts and yelps of teenage boys amusing themselves.

It all seemed so normal; it all was so normal. So much so that, when a prayer mat and textbooks on the Qur’an appeared on a shelf in his room, it came as something of a surprise. His father and I discussed his conversion between ourselves but, naively, we saw it as cosmetic change. This was, we reasoned, our boy’s version of going punk or vegan for a few months. We believed that this ‘conversion’ would be a harmless passing phase. We were wrong.

Over the next few months we saw the boy we knew become buried beneath a spiritual totalitarianism. The word Islam means submission. It allows you to love nothing else; to be a good Muslim, you must surrender yourself completely. Under the informal tutelage of his new friends, our boy eagerly took on the attitudes of his Muslim ‘brothers’ in place of his former personality. Why, he protested, didn’t I cook every night? Why didn’t I ‘look after’ him and his dad like a good (Muslim) woman would? I was lazy, I was ‘irresponsible’, he would say, a smug little smile on his face. I felt angry and sad.

To keep the peace, I tried to take it as a joke, informing him that I had a career that involved more than just having babies. Gradually though, I found myself worn down by his attitude.

It wasn’t just women who found themselves at the sharp end of our boy’s new found sagacity. A news story about Afghanistan prompted him to join in our discussion of politics, something which in the past had been of no interest to him. He informed us that the problems in the region were the fault of ‘The Jews’; everything bad in the world could be laid at the door of ‘The Jews’. The Holocaust never happened, he insisted, but in the same breath he would say that ‘the Nazis should have finished them off’. ‘The Jews’ had caused the world financial crisis and, of course, ‘The Jews’ were the reason why he couldn’t find work. It was not because he had neither qualifications nor work experience, although that was probably their fault too.

Before his conversion, we had together watched Four Lions, the Chris Morris comedy about young British jihadis, and laughed at the idiotic prejudices of the white convert character, Barry. Now our normal teenage boy had been replaced by a caricature. We challenged him, thinking reasonableness would see him acquiesce. But we were not dealing with a rational mind. Our Muslim boy would heed no evidence against his argument and neither did he require any evidence to justify his prejudices. He just shook his head at our ‘blindness’, our blasphemous absence of faith. We’d see, he said, the familiar smug smile appearing: it was all in the Qur’an. We should convert before it was too late.

Some of you reading this might dismiss me as a bigot, prejudiced against a religion I do not understand. But please ask yourselves how you would feel if your child started spouting hate-filled bile against homosexuals, women, Jews, anyone in fact, who wasn’t a Muslim man? Every day we fought, struggled, wept and grieved for the boy. All we wanted was our son back.

Two years later, we have started to make some progress. Every day he returns to us a little more. His eyes have light in them again. It’s almost as if he is recovering from some disease. He explains his reversion succinctly: ‘I realised that I was good enough, that I didn’t need to follow someone else’s idea of what I should be.’ He can now take responsibility for his life rather than seeking to blame others. He is maturing. He no longer needs the support of a tribe, which is what attracts Muslims from all backgrounds and nations to the idea of jihad. I’ve come to think that it is youth, not persecution or poverty, that these Islamic State groupies have in common, an embryonic sense of identity. For them, blaming America for the world’s problems is the equivalent of shouting at their parents that they ‘never asked to be born’.

Every time I hear of another young man who has lied to his family and gone to join the carnage in the Middle East my heart breaks. You can, if you choose to, ignore the problem of the Muslim radicalisation of our youth in the mosques and on the streets. It is, after all, so easy to tolerate what does not immediately affect you, and it’s nice to feel that one is liberal about Islam. But the lesson I’ve learnt is that we’re going to have to fight for our progressive democracy, because although you may tolerate Islam, Islam might not tolerate you. When it lives in your house, eats your food, sleeps under your roof, enjoys all the comforts you provide, all the while despising you, then you will be forced to make a choice.