Members of the audience had to make up their minds whether to vote with their heads or their hearts as five eminent scientists battled it out during the exciting evening organised by the international environmental charity.

An initial vote put Professor David Thomas in the lead with plankton, followed by Dr. George McGavin representing bees; then the pair were each given another five minutes to win over support for their species – and everything changed.

Professor Thomas presented a superb summing up, but the outstanding winner, Dr. McGavin, won the day with his persuasive argument, explaining how one quarter of a million species of flowering plants depend on bees. He added that many species are crucial to world agriculture, and without them, we would lose not only flowering plants, but many fruit and vegetables. Among the major causes of bee declines are habitat loss and fragmentation, increasing use of insecticides, and diseases.

Dr McGavin said, ‘Bee populations are in freefall. A world without bees would be totally catastrophic.’

Television broadcaster Andrea Catherwood chaired the ‘Irreplaceable’ debate. She told the audience, ‘So in household terms on Christmas Eve with the family about to arrive, think oven rather than ornaments, dishwasher not designer handbag. We’re looking for the species we’d be hardest pushed to live without.’

The other speakers who didn’t make the top two, but nevertheless produced convincing arguments, were Ian Redmond OBE representing primates, Dr. Kate Jones fighting for bats, and Professor Lynne Boddy arguing for fungi.

These annual debates, which are designed to both inform and entertain, are now in their eighth year, and have become a highlight of the conservation calendar. Previous themes have ranged from endangered ecosystems to invasive species. They form part of Earthwatch’s educational mission to engage people in the most pressing environmental challenges facing our planet today.

The debate will be broadcast at 8pm on Radio 4 on Christmas Eve. For more information visit www.earthwatch.org./europe

The Earthwatch events programme is kindly supported by the Mitsubishi Corporation Fund for Europe and Africa.