Environmentalists including Chris Packham and Bear Grylls have urged Britain to drop its support for polar bear trading – claiming that the UK's opposition to a ban has contributed to thousands of the animals being hunted for rugs, trophies and body-parts.

Although the polar bear's survival is threatened by the melting of its Arctic sea-ice habitat, it is still legal to hunt the animals in Canada.

Wealthy tourists from as far afield as China pay up to $20,000 to track and hunt the endangered bears on dog-sledges, with more than 32,000 specimens traded internationally between 2001 and 2010. Skins, skulls and even teeth are sold, predominately in Japan and within the EU.

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The UK has previously backed looser regulation of the trade, which has resulted in around 600 polar bears being shot in Canada every year, as well as an unknown number being shot illegally in Russia.

In a letter seen by The Independent, the Humane Society International urges Richard Benyon, the Wildlife minister, to "be a champion for the polar bear" by voting for a ban on the lucrative global trade in polar bear body-parts at a key meeting of the Convention on International Trade in Endangered Species (Cites) later this year.

The letter has als o been signed by Mr Packham, the adventurer Mr Grylls, and the actors Joseph Fiennes, Brian Blessed and Martin Clunes, in addition to the actress Joanna Lumley and the biologist Mark Carwardine.

The USA, backed by Russia, has proposed upgrading the polar bear's Cites trade status from Appendix II to Appendix I, which is reserved for the planet's most endangered species and would impose an effective ban on trade in polar-bear products. At the last Cites summit in 2010, the UK led the EU bloc of 27 nations in voting for lighter Appendix II regulation – a position conservationists say must be urgently reversed.

"The survival of the polar bear is threatened like never before from habitat loss through climate change," reads the letter, which is signed by Mark Jones, the head of the Humane Society International. "Whilst action we take now to tackle climate change may take years to benefit polar bears, ending the global trade will give them immediate and much-needed respite."

The next Cites summit will be held in Bangkok in March. If a two-thirds majority of nations votes in favour of tighter restrictions, an effective ban on polar-bear trade will become international law. In 2010, the 27 EU votes were crucial in blocking a ban, with 48 voting for and 62 against out of 121 nations. The UK is seen as a key voice in swaying the EU bloc vote.

Scientists estimate that there are between 20,000 and 25,000 polar bears left in the wild, with two-thirds of them found in Canada. Of the 12 populations for which data exist, eight are in decline. The decreasing extent of the Arctic summer sea-ice as a result of global warming has put extreme pressure on the species, robbing it of its main hunting ground. According to models created by the US Geological Survey, the bears could lose 70 per cent of their habitat by the middle of the century.

A spokesman for Mr Benyon's department, Defra, said that policy advisers were "considering the proposals" on a trade ban, adding that Mr Benyon would not be personally attending the Cites meeting in Bangkok. The spokesman said that, with the threat of climate change, trophy-hunting had been considered a secondary threat to polar bears and legislating for it was like "fiddling while Rome burns".