Alex Batty, a British teen who went missing six years ago and was found this week in southwest France, boarded a plane home on Saturday, the Toulouse public prosecutor told AFP.

The 17-year-old boarded a KLM flight to the UK via Amsterdam, "accompanied by British police officers", said assistant prosecutor Antoine Leroy.

Batty will be returned to his maternal grandmother, with whom the British justice system entrusted his custody before his mother abducted him, aged 11, in 2017 while on holiday in Spain.

For six years, including two in France, he lived a "nomadic" life in a "spiritual "community", never staying more than several months in the same place.

The teen was found walking along a village road in the early hours of Thursday morning by a delivery driver four days after he escaped, a deputy prosecutor told journalists. 

He is in good health and does not appear to have been abused in the years since his abduction, according to the doctor who examined him.

His mother, Melanie Batty, has yet to be found and could be in Finland, Leroy said.

Alex told French investigators they spent time in Morocco before moving to the French Pyrenees, along the border with Spain.

A spiritual community

Alex told investigators that he had spent time in a spiritual community centre focused on "work on the ego, meditation and reincarnation", the prosecutor said.

It was when his mother decided to move to Finland that he decided to escape, Batty told investigators.

He had been walking along the road by night to avoid detection, foraging food from gardens and fields along the way.

It was Fabien Accidini, a student working as a delivery driver, who picked him up on a road between two villages in the pouring rain in the small hours of Thursday morning.

"He clearly needed help," he told AFP, and since Alex did not speak French very well, he spoke to him in English.

"He was a bit suspicious at first," he added, initially giving a false name. But as the boy helped him with his deliveries to local pharmacies, he began to open up.

"When he told me he'd been abducted, I made him say it again - it was crazy!" said Accidini.

He lent him his mobile phone so he could contact his grandmother in England via Facebook to tell her he wanted to come home, and then he got in touch with the gendarmes.

While they were waiting for them to arrive, Accidini entered the boy's real name into the internet. "I typed in his first and last name and saw his photo, which was the same as his face today at 17."

Alex told him he hoped to go back to school and study to become an engineer, he added.

"He had a good head on his shoulders," said Accidini.

"He knew that where he was was not real life - and that he didn't want that life in the future."

Alex Batty told investigators he had not suffered any physical violence during the past six years.