Time is running out to save some of Britain's best loved insects, a wildlife charity is warning.

More British butterflies are now facing extinction than ever before according to the latest in-depth assessment of populations.

Wildlife charity Butterfly Conservation says 24 species are now listed as threatened - including eight classified as endangered - with the risk of extinction increasing for more species than decreasing.

Using data gathered by volunteers through the UK Butterfly Monitoring Scheme and Butterflies for the New Millennium recording scheme, scientists have put together a new Red List, which assesses all the butterfly species that have bred regularly in Great Britain against the rigorous criteria of extinction risk set out by the International Union for Conservation of Nature.

Of the 62 species assessed, four are now extinct in Britain, which are the Black-veined White, Large Tortoiseshell, Large Copper, and Mazarine Blue.

A further 24 - or 41% of the remaining species - are classed as threatened with eight classified as endangered, 16 vulnerable and a further five listed as 'near threatened'.

Among the eight endangered is the Black Hairstreak, Wood White and Wall butterflies while booth the Large Heath and the Grayling species of butterfly have also now moved from vulnerable to endangered, and seven species have moved from near threatened to threatened, including the Swallowtail and Adonis Blue.

Two new species have been added to the list for the very first time, Scotch Argus, which is listed as vulnerable, and the Dark Green Fritillary, listed as near threatened.

Head of Science for Butterfly Conservation, Dr Richard Fox, said: "Shockingly, half of Britain’s remaining butterfly species are listed as threatened or near threatened on the new Red List. Even prior to this new assessment, British butterflies were among the most threatened in Europe, and now the number of threatened species in Britain has increased by five, an increase of more than one-quarter.

"While some species have become less threatened, and a few have even dropped off the Red List, the overall increase clearly demonstrates that the deterioration of the status of British butterflies continues apace."

At the beginning of May, the Kent Wildlife Trust warned that there had been a 'terrifying fall' in the number of flying insects in the county according to a Bugs Matter survey and called for urgent action to try and reverse the decline.

Changes to how land in Britain is being used is thought to be the most important driver behind the ongoing decline of butterflies but the impact of climate change is also now starting to become evident, say experts, who are noticing butterflies having to adapt to cooler or damper climates.

But among the gloomy predictions is some good news.

The Large Blue butterfly, which became extinct in Britain in 1979 has been subject to an intensive, ongoing and successful reintroduction programme which has been it now move from being classified as critically endangered to near threatened. The High Brown Fritillary, also formerly listed as critically endangered, has moved to endangered; likely to be the result of intense conservation work from Butterfly Conservation alongside other organisations.

The Duke of Burgundy and Pearl-bordered Fritillary, which have also benefited from much targeted conservation effort, both moved from endangered to vulnerable.

Dr Richard Fox added: "Where we are able to target conservation work, we have managed to bring species back from the brink, but with the extinction risk increasing for more species than are decreasing, more must be done to protect our butterflies from the effects of changing land management and climate change.

"Without action it is likely that species will be lost from Britain’s landscapes for good, but Butterfly Conservation is taking bold steps to improve key landscapes for butterflies and reduce the extinction risk of many threatened species."