This report has been produced as part of the JNCC Species Status Assessment project, assigning conservation status to British flora and fauna using internationally approved IUCN Red List criteria and categories.  Within this project, the remit of the present report is to assess the status of butterflies throughout Great Britain, using the updated IUCN Red List criteria and categories (IUCN, 2001).

The first Red List assessment of butterflies in Britain was produced by Shirt (1987) using the original IUCN criteria.  Warren et al (1997) produced a Red List assessment of British butterflies using later IUCN criteria that included the rate of decline, as well as rarity, to assess threat.  More recently, species have been prioritised for conservation action through the UK Biodiversity Action Plan process (Bourn et al, 2005, UK Biodiversity Group, 1998), using criteria such as international importance, rate of decline and other important issues (see Warren et al, 2007 for overview).

Since the last two Red List assessments of butterflies in Great Britain, a great deal more detailed information on their distribution has become available through the publication of The Millennium Atlas of Butterflies in Britain and Ireland (Asher et al, 2001) and subsequent recording.  Comprehensive new data on both distribution trend and population trend were published in The State of Butterflies in Britain and Ireland (Fox et al, 2006), allowing an up-to-date and comprehensive assessment.  It is clear from these data that the status of many butterfly species has changed since the first reviews and a reassessment of their Red List categories is now due.  This report contains the first assessment of British butterflies against the new IUCN criteria, which now include far more explicit and quantified criteria (IUCN, 2001, 2003).  Butterflies are known to be one of the most rapidly declining groups of plants or animals (Thomas et al, 2004) so the report is both important and timely.