An aid worker from Leeds, who was caught while trying to smuggle an Afghan girl into the UK, will plead guilty before a French court for the crime. Rob Lawrie, a former army physical training instructor, was approached by the child's father to rescue her from the migrant encampment in Calais, France in October 2015.

The 49-year-old, after repeated pleas from the girl's father – to take her to her relatives in Leeds –decided to help them. The Brit father-of-four was caught at the Calais border the following month, when authorities along with sniffer dogs inspected his vehicle. Two Eritrean men had also sneaked into the car to escape to the UK.

When the two men were found, Lawrie was immediately handcuffed and taken into custody. After his arrest, he told authorities to go back to the van to find the girl. Describing his decision to transport the girl as a "moment of madness", Lawrie said: "All rational thought left me. I thought, how can I leave this little girl here.

"There's a family there that can pay for her, educate her, love her, house her. She'll have her own bedroom. Or, I can give her back to her dad who's going to put her back in a cold shelter and carry on living like that," he added.

After deciding to plead guilty, the ex serviceman said that he was "preparing for the worst and hoping for the best". The French court will decide the quantum of sentence in a hearing on 14 January.

Lawrie was working at the Jungle Camp, helping build shelters, when he got to know the four-year-old Bahar Ahmadi known as Bru and her family. "The conditions at the camp were horrendous and I knew she shouldn't be living like that. Morally and compassionately I was getting this little girl out of severe danger to a family that could love her, pay for her, educate her," he said.

What would have otherwise seemed like a case of kidnapping, turned into smuggling, when Bru ran to Lawrie to give him a hug while at a detention centre. The former Royal Corps of Transport soldier is facing a maximum sentence of five years in prison or a €30,000 (£22,560/$32,743) fine. He will appear before magistrates in Boulogne where he said he will plead guilty but is hopeful for a lighter sentence.

"What I did was highly wrong. It was done on the spur of the moment. It was done in a mind that had no rational thinking going on. Any volunteer that's been in one of these camps for a period of time will tell you that rational thoughts just leave you, just don't exist," he explained.

Lawrie wanted to volunteer as an aid worker after seeing an image of the Syrian toddler Aylan Kurdi, who had drowned and his body washed up on a beach in Turkey. "It was that moment that took me from being a passive supporter of refugees to an active supporter of refugees," he said.

"It's more unfair to have people living like that than for me to spend five years in prison."

A petition has been signed by thousands of friends, family and empathisers requesting Foreign Secretary Philip Hammond to ask the French authorities for clemency.

Since his arrest, Lawrie has separated from his wife, lost his job and a considerable amount of weight, and has become bankrupt. "I have been destroyed mentally and holistically. But I still say I broke the law," he expressed.