They say Britain is only a third of the way towards meeting key targets under the UN biodiversity convention for protecting native plants.

In March, a UN report concluded that virtually all indicators of the future diversity of life on Earth are “heading in the wrong direction”.

The Global Biodiversity Outlook (GBO) said that “unprecedented efforts” would be needed to achieve the internationally-agreed aim of slowing the decline in species richness by 2010.

The groups behind this week’s Kew meeting – the government’s Joint Nature Conservation Committee (JNCC), the charity Plantlife International and the Royal Botanic Gardens itself – paint a similarly grim picture for Britain’s plants.

Their warning comes a few days after another major report found that many UK plants are being affected by climatic change, nitrogen pollution and introduced species.

The concern is slow progress towards targets set by the government in its Plant Diversity Challenge, its response to the UN’s global strategy.

“We are really falling behind on targets for ensuring that plants are used sustainably, and for conserving threatened plants,” said Chris Cheffings, plants adviser to the JNCC.

“We will need a wide-ranging commitment across the board if we are going to have things back on track by 2010, and that will mean more than just botanists working together to achieve the targets.

“We need to step up our efforts to communicate the plight of plants and fungi to all sectors of society.”