By Matthew Champion.

A giant rat – possibly the world’s largest – is among 40 new species discovered by a BBC documentary team in a remote volcano crater in Papua New Guinea.

The Bosavi woolly rat, which weighs 1.5kg and measures 82cm from nose to tail, showed no fear towards any of the scientists or cameramen, suggesting it had never encountered humans before.

The cat-sized rat was found in the crater of the extinct volcano Mount Bosavi during filming for Lost Land of the Volcano, a three-part series which starts on BBC1 tomorrow night.

Led by climber and naturalist Steve Backshall and including wildlife cameraman Gordon Buchanan and scientist Dr George McGavin, the team climbed into the 4km wide crater in January, spending three months in the rainforest inside.

The Bosavi woolly rat, named after its silvery grey and dense fur, is believed to be largely vegetarian, nesting underground or in tree hollows.

Team member Dr Kristofer Helgen, a Smithsonian biologist, said: "This is the one of the world’s largest rats. It is a true rat, related to the same kind you find in the city sewers, but a heck of a lot bigger."

Mr Buchanan added: "I had a cat and it was about the same size of this rat. This rat was incredibly tame. It just sat next to me nibbling on a piece of leaf. It won’t have seen a human being before. This crater of Mount Bosavi really is the lost world."

Among the 40 other new species the team believes it discovered was the marsupial Bosavi silky cuscus, which also showed no fear of man.

A camouflaged gecko, a fanged frog and a grunting fish are also awaiting official classification as new species.

Lost Land of the Volcano, the first of three one hour-long shows, starts tomorrow at 21:00 BST on BBC1

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