The father of a Muslim convert, who left Oxford to live under Islamic State, blamed himself and begged his son not to risk his life and “leave us only photos”, a court heard.

In an emotional email John Letts, 58, an organic farmer, told a friend he felt he had “lost” his son, Jack, now 23, who was believed to be in Syria.

“I thought I’d seen some shit in my life … but this is as bad as it gets,” wrote Letts, in exchanges read to an Old Bailey jury.

“I feel terrified, betrayed by Jack, embarrassed, massively let down. I know he’s not a nasty boy. But he’s very stupid. And I created him with my armchair revolutionary shite.”

Letts described the impact on Jack’s mother, Sally Lane, 56, as the couple did not know if their son was dead or alive. “Sally’s not coping. She’s quitting her job, sleeps with the phone in her hand waiting for the dreaded call or text or email.”

He continued: “Why do people believe in fairy tales and die for them? What did I do so wrong? Don’t waste any time my friend. Spend every minute with your kids. You never know what will happen.”

Letts and Lane, from Oxford, are accused of sending or attempting to send their son a total of £1,723 after he travelled to Syria.

The couple, who are charged under section 17 of the Terrorism Act 2000, deny three counts of sending or attempting to send money between September 2015 and January 2016. The prosecution claim that from information available to them at the time, they “knew or had reasonable cause to suspect” that the money might be used to fund terrorism.

The jury heard they had believed their son was attending an Arabic course in Kuwait, but then discovered he was headed for Syria.

In one Facebook post, his father implored his son: “Why haven’t you at least contacted us to explain, Jack? I miss you so much and look at your photo all the time. Please don’t leave us only photos, Jack. Life is to be lived.”

In another, he wrote: “Jack, please call. Your mother is crashing badly and so am I. We are suffering. Please phone, Jack.”

After discovering he might be in Syria, Letts wrote to one friend: “I fucked up big time. Sally and I are destroyed and ashamed. He’s not contacting us. Not sure if he’s dead or alive. My turn to feel the pain of war, my brother.”

To Jack, Letts wrote: “Your life here with me went too fast, my boy. One day I had a funny, generous and happy little son who made me laugh, sang rock and roll, wrestled with me on the sofa … always made me proud to be a dad.

“And he changed so quickly and left with barely a goodbye”.

Letts continued: “The light that filled our lives went out when you left. Now we wait for a phone call and check Facebook constantly to see if you’re still alive.”

Referring to the fact Jack had got married in Iraq, Letts wrote: “Can she cook?” He added: “Is she kind, gentle, funny? I dreamed for 18 years of seeing you married. I had a gift I was going to give you from my dad for the moment.

“Please give my love to your new wife. I hope I will meet her one day, and I hope that you get the chance to love and laugh and play with your little boys (or girls) as much as I did. Dad.”

In further exchanges, Letts vehemently challenged his son’s beliefs and questioned the hurt he had caused his parents. “I suppose we’re just nasty, unbelieving western kafir [non-believer] enemies of Islam who need to be wiped out before your new utopian caliphate begins. I really thought you were more clever than this.”

Letts adds: “I don’t expect you’ll ever write to me again, son. But then I don’t think you care about me or us any more, or care if you see us again. I feel I’ve lost you and if I could forget I had a son called Jack, this pain would stop.

“But I can’t and I never will. I will stand here beside your mother and suffer with her until the end.”

The court heard Jack Letts had been “personable , engaging and humorous” before converting to Islam aged 16. His performance at school suffered due to his obsessive compulsive disorder his father said in a police statement. “He had a phase of being obsessed with football and would sleep next to his football,” his father told police in 2015.

“The same thing happened with religion.” He said Jack would “read all things to do with Islam”.

The case continues.