A British explorer and University of East Anglia (UEA) alumnus who went missing on an expedition to reach a remote tribe in Papua New Guinea has been seen alive and well, reports say.

Benedict Allen, who has no mobile phone or GPS device with him, was dropped by helicopter in the remote jungle three weeks ago.

He was hoping to reach the Yaifo, a tribe thought to be one of the last on Earth to have no contact with the outside world.

His friend, BBC security correspondent Frank Gardner, tweeted: 'UK explorer @benedictallen has been sighted, 'alive and well' nr airstrip in Papua New Guinea after being reported missing while trekking.'

Mr Gardner travelled to Papua New Guinea with Mr Allen twice last year.

Mr Allen, 57, was due to return to the capital, Port Moresby, on Sunday, before returning to Britain.

Next Tuesday, Mr Allen was due to speak about his trip at a Royal Geographical Society event at the Guildhall of St George, in King's Lynn.

He was due to appear with Mr Gardner at the event, which is part of Lynn Festival's year-round series.

Mr Gardner said: '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 post on his website before setting off, Mr Allen said: 'No outsider has made the journey to visit them since the rather perilous journey I made as a young man three decades ago.

'This would make them the remotest people in Papua New Guinea, and one of the last people on the entire planet who are out-of-contact with our interconnected world.'

His agent Joanna Sarsby said: 'He is a highly experienced explorer, very clever and resourceful and adept at surviving in the most hostile places on Earth, and he would never give up.

'He was trying to reach the Yaifo people, a very remote and reclusive tribe - possibly headhunters, quite a scary bunch. Goodness knows what has happened.'

Mr Allen studied environmental sciences at UEA wand went on expeditions to a volcano in Costa Rica, a remote forest in Brunei and a glacier in Iceland.

On UEA's alumni webpage, he said: 'At school I knew I wanted, one day, to go out and explore the world - but at the same time communicate it. UEA was my first choice of university, because it was modern and in touch.

'I chose to read environmental sciences because I hoped it would give me an informal base from which to launch out and achieve all I'd dreamt of. This it did.'