A British explorer is believed to be missing after failing to return from an expedition searching for a remote tribe.

Authorities have launched a search for Benedict Allen who has not contacted home since travelling to Papua New Guinea three weeks ago.

The 57-year-old, who has a home in west London, was expected to travel back on the weekend after his venture to meet the Yaifo tribe.

He first travelled to the tribe's home in the southwestern Pacific 25 years ago and hoped to be reunited with them.

The author and TV presenter, who has made six TV series for the BBC, has no mobile phone or GPS device with him, but his family are said to be extremely worried.

Mr Allen travelled to Papua New Guinea three weeks ago. Credit: PA

Mr Allen's family raised the alarm after he failed to return to from his trip by Monday.

He has been described as a "highly experienced explorer, very clever and resourceful".

But his family conveyed their worry for his welfare on Wednesday.

Mr Allen's sister Katie Pestille said: "He knows all about that survival stuff. It's just what worries me is there are bad people in these jungles.

"You would think that they were totally empty but there are people in there. I mean, I know more about the Amazon, but there are loggers and drug dealers and all sorts of bad people."

Mr Allen's friend, BBC security correspondent Frank Gardner, who travelled to Papua New Guinea with him twice last year, said: "I would say the chances are that Benedict is going to be fine, I hope those aren't famous last words.

"Benedict always expected something like this. I had supper with him just before he left and he said, 'look, I'm quite certain I'll probably be out of contact for quite some time and people shouldn't worry about it'."

In a blog post on his website, Mr Allen wrote in September: "The Yaifo are one of the last people on the entire planet who are out of contact with our interconnected world.

"In October I'm hiring a helicopter to drop me off at the abandoned mission station, Bisorio - a forlorn place.

"Last time the Yaifo greeted me with a terrifying show of strength, an energetic dance featuring their bows and arrows.

"On this occasion who knows if the Yaifo will do the same, or run off, or be wearing jeans and T-shirts traded eons ago from the old mission station."

A Foreign and Commonwealth Office spokesman said: "Our staff are assisting the family of a British man who has been reported missing in Papua New Guinea, and are contacting the local authorities."