The prosecution of the parents of a young Muslim convert dubbed Jihadi Jack has been described in court as “inhumane to the point of being cruel”.

Organic wheat farmer John Letts, 58, and his former Oxfam fundraiser wife Sally Lane, 56, from Chilswell Road, Oxford, are on trial at the Old Bailey accused of funding terrorism.

They allegedly sent or tried to send £1,723 to their son Jack Letts after he travelled to Syria in 2014 aged 18.

Jurors have to decide whether a person would reasonably have suspected the money would go to terrorism and whether the couple acted “under duress” believing their son was in immediate danger at the time.

In a closing speech, John Letts’s barrister Henry Blaxland QC told jurors: “It’s important in this case we do not ask you to differentiate between John Letts and Sally Lane. There are some evidential differences. The obvious one is John did not send the money.

“He had a less good understanding of what was going on because he was working on the farm. We are not going to suggest that he was not supportive of what Sally did at the time. He understood what was going on.

“He supported it then and he supports it now and it’s important you understand.”

He told the court the defendants were supportive of the battle against terrorism.

“But this prosecution does absolutely nothing to further the prevention of terrorism. In fact it runs the risk of undermining the fight against terrorism because it runs the risk of bringing the law into disrepute.

“This prosecution is completely inhumane to the point of being cruel. These parents have to all intents and purposes lost their son.

“They are having to deal with that. They are having to deal with the trauma.

“Law without compassion is not justice and there is no compassion at all in the approach to the evidence in this case. If you approach this without compassion you run the risk of having a completely blinkered view.”

He told jurors the couple had been “let down” by the authorities and given “contradictory advice by the people they turned to for help”.

Earlier, Tim Moloney QC, for Lane, had told jurors police advice the defendants were given about sending money to Jack Letts in December 2015 was not as clear and unambiguous as the prosecution claimed.

On December 27 2015, a family liaison officer sent an email saying John Letts had been “informed they can send Jack funds if there is a genuine belief he needs assistance to leave Syria”.

The officer went on: “I have made it clear they need to capture all their communications with Jack and remain completely open with us.”

Mr Moloney said: “How is that not permission?”

He told jurors that follow-up advice to the couple three days later was “not clear and unequivocal”.

In a written notice, the defendants were told: “The police do not endorse or authorise the sending of any monies to Jack Letts.”

While the decision whether or not to send money “rests with them”, they warned they could be liable to be committing an offence.

The notice added: “Any decision to leave where Jack is currently residing would be at his own risk.”

He told jurors the defendants did not reasonably believe they were funding terrorism by sending money, given what they knew about their son, who has obsessive compulsive disorder and Tourette’s.

He said: “They would not have sent it if there was a chance it would go to IS (Islamic State). They hated Isis.

“They were faced with a terrible dilemma. It was clear their son’s life was at stake, the threat to his life coming from the very organisation where their son was and they hated.”

“They knew the risks they faced and they were prepared to take the risk to save their son.”

John Letts, who declined to give evidence in his defence, and Lane, from Oxford, deny the charges against them.