MPs say the government must take responsibility for protecting the unique species and habitats of its isolated island territories

The string of isolated island territories making up the last vestiges of the British empire host a treasure trove of exotic species but are inadequately protected by the UK government, an MPs' report warns.

The UK's overseas territories (UKOTs) include huge tracts of ocean, thousands of coral atolls, tropical forests and a vast polar wilderness, and stretch from the Cayman Islands in the Caribbean to the Pitcairn Islands in the Pacific.

Despite the UKOTs accounting for 90% of the biodiversity for which the UK is responsible, MPs on the environmental audit committee (EAC) found that just 0.3% of the government's biodiversity conservation budget was spent there, while weak rules meant housing and new airports threatened unique habitats and invasive species went unchecked.

Some species in the territories are clinging to life, such as the Ascension predatory shrimp, whose global population is confined to just two rockpools, and the red berry tree in the Pitcairn islands, of which just four individuals remain.

At least 500 globally threatened species live in the UKOTs, including the blue iguana, rockhopper penguins a giant spiky woodlouse confined to St Helena, vivid lorikeets and the resplendent angelfish, found only on Ascension.

The globally threatened Henderson lorikeet is one of the five unique bird species found on the UK's world heritage site on Henderson Island, part of the Pitcairn overseas territory in the Pacific Ocean. Photograph: Tara Proud/RSPB

The blue iguana, which lives in the Cayman Islands in the Caribbean, has recovered from just 12 survivors in 2002 to 750 now. But it remains seriously threatened by a planned motorway that will go right through the remaining stronghold.

"The natural environment in the UKOTs is incredibly diverse, but it is currently underprotected," said EAC chair, Joan Walley. "That is ultimately a UK government responsibility. But the UK government doesn't even know precisely what it is responsible for, because it has failed accurately to assess and catalogue those species and habitats."

She added: "During our inquiry, the UK government expressed vague aspirations to 'cherish' the environment in the UKOTs, but it was unwilling to acknowledge its responsibilities under UN [biodiversity] treaties."

Ministers had exercised power when it came to the tax affairs of UKOTs, but did not do so to protect biodiversity, Walley said.

Tim Stowe, the RSPB's international director, said the government must play its part in curbing extinction of species: "The far-flung UKOTs are jewels of conservation."

A government spokesman said: "We take the biodiversity of our overseas territories seriously. Since 2010 we have committed over £6 million to helping UKOTs protect their biodiversity."

The 14 UKOTs span the globe and as a result feature an extraordinary range of endangered species. The southern UKOTs, including the British Antarctic Territory and Falklands, mean UK is responsible for more penguins than any other nation, but 2 million pairs of northern rockhopper penguins have disappeared from the territory of Tristan da Cunha in the last 60 years. Sperm whales and southern elephant seals also appear in these southern UKOTs.

The Wilkins's bunting , down to its last 80 pairs in the Tristan da Cunha, along with 31 other endangered bird species mean the UKOTs have more species at risk than the entire continent of Europe.

In the Pitcairn group of Pacific islands, there are more endangered species than people living there, 70 versus 50. The Henderson lorikeet is one of the five unique bird species found on the threatened UK world heritage site of Henderson Island, part of Pitcairn.

In the Atlantic, the endangered green turtle depends on the Ascension Islands, its second most important nesting in the ocean, while on St Helena, there are just 50 spiky yellow woodlice left, in a remnant of cloud forest no bigger than a tennis court.

Off Bermuda, the mysterious and endangered European eel is thought to breed, before beginning its transoceanic migration, while the critically endangered mountain chicken – actually a massive carnivorous frog – has an important stronghold on Montserrat.

The MPs found illustrative examples of the difficulties faced in the UKOTs during a visit to the Cayman Islands. They discovered a plan for 200 houses on Little Cayman, an island 10 miles long and one mile wide with a population of 170. It hosts the largest population of red-footed boobies in the Caribbean and is a designated wetland of international importance.

The MPs also found that virtually nothing from a £40m Caymans environment protection fund – raised from tourists – has been spent on environmental protection and that a state-run turtle farm – most of which were eaten – received an annual subsidy four times greater than the entire annual budget of the islands' department of environment.

Walley said that while the UK government had constitutionally subcontracted environmental management to the governments of the 11 inhabited UKOTs, that did not absolve Westminster of its ultimate responsibility under international treaties it had signed on the UKOTs' behalf.

She said it was not acceptable for the Foreign and Commonwealth Office to renounce its responsibility to ensure that good governance arrangements exist in the UKOTs.

Note: A comment from a government spokesman that was not available for the original version of this article has been added.