A British hiker who went missing on a solo trek in the Pyrenees mountains was given a lift by a mystery man three days before she vanished.

A Facebook post by adventurer Esther Dingley revealed she accepted a lift from a fellow hiker after bad weather forced her to change her plans.

Police are reportedly keen to track the man down.

The 37-year-old set out last month to trek from the Port de la Glere to the Port de Venasque, a route which follows the border between France and Spain.

But it appears she eventually opted to head back down the valley to where her camper van was parked and re-jig her route, according to the post on November 19.

Dan Colegate, 38, said police are exploring the possibility Esther did not have an accident

She was due to meet her boyfriend Dan Colegate, 38, at a farm in Gascony he had been staying at during their month apart on Wednesday, but never showed.

"I had the option of staying at a great cabin, even had a mattress, but it was only 2pm or going down with my fellow hiker and getting a lift," Esther wrote.

"He'd take me further up the valley so I could continue my planned tour to another refuge or back to the camper..."

Esther revealed in a Facebook post she accepted a lift off a fellow hiker

The mystery man is thought to have dropped Oxford University graduate Esther off at Benasque on the Spanish side of the mountain range where police found her van.

An investigative source in Spain told The Sun: "This man would have had conversations with her and may know what she planned.

"They may have arranged to meet and hike another route. It is imperative that we find him."

Mobile phone signals are said to be crucial in finding out what happened to Esther after Dan said police had begun looking at options "beyond an accident", following an extensive search of the trek route and mountains.

She was due back from a month-long trek on Wednesday

Esther and Dan have been travelling throughout Europe since 2014, with the "prevailing opinion" of authorities being she is not in the mountains, following extensive searches.

She last had contact with Dan over a week ago when she sent him a selfie atop the 8,983-ft Pic de Sauvegarde at 4pm on November 22.

She had started walking from Benasque the day before.

Her plan had been to descend the peak, then walk the eight miles from Port de la Gléré to Port de Venasque, before hiking down from the mountains on Wednesday.

Dan reported her as missing the day before she was due back.

Esther is now listed as a national missing person in Spain and her case has been passed to "a specialised judicial unit in France", Dan added in a post on Facebook on Tuesday.

"For several days now there has been talk that perhaps Esther might not be up there and that this was the reason they couldn't find her," he wrote.

Dan went on to say, taking into account Esther's high level of experience and the nature of the terrain, as well as the good weather and the fact she was on a clearly defined route, the "prevailing opinion" is she is not still on the mountain trail.

"That if she had fallen from one of the paths, they really would have expected to find her given the intensity, the closeness of the search and the fact most of the trails are really quite straightforward across open ground," he added.

The extensive search efforts undertaken by units from both countries have utilised helicopters, dogs and a drone.

The couple, from Durham, started to travel after Dan recovered from a flesh-eating virus and had been documenting their camper van adventures online.