A new Red List of British butterflies outlines 23 species which are already extinct here or whose numbers have dropped to such low levels that they are vulnerable to extinction.
The High Brown Fritillary is one of two species rated as Critically Endangered. This species has been the fastest declining of all British butterflies seeing numbers drop by 85% over a 10-year period.
The research confirms that butterflies are not only a highly threatened group in Britain but that they are faring worse than dragonflies, birds and plants. Twenty three species - 37% of all our native butterflies - are considered to be regionally extinct or threatened.
This compares to 21% of dragonflies, 29% of birds and 20% of plants. A further 11 butterfly species are classified as 'near threatened' in the new Red List, leaving fewer than half (45%) of Britain's butterflies considered to be safe at present.
The figures are the result of a major re-assessment of the state of British butterfly populations using the International Union for Conservation of Nature (IUCN) Red List approach.
It is based on data collected by thousands of volunteer recorders coordinated by the charity Butterfly Conservation and the Centre for Ecology and Hydrology. The results are consistent with previous evidence of butterfly trends and confirm that butterflies are a highly threatened group in Britain.
"The new Red List shows that the number of butterflies in need of our help has increased dramatically in the past 10 years," says Richard Fox from Butterfly Conservation, who is lead author of the study.
"We have already seen conservationists bring the Large Blue butterfly back from extinction but there is so much more we need to do to secure the future for our fastest declining species. They are our heritage."