A painted lady butterfly, this is a summer migrant to the UK and according to UKButterflies.co.uk there are large numbers migrating in from continental Europe, originating from Morocco. The right weather conditions in Africa and Europe and the recent good weather in the UK could result in possibly the biggest for migration for decades.
The Butterfly Conservation website has a survey for these and migrant butterflies (http://www.butterfly-conservation.org/sightings_home/1095/migrant_watch.html) and these two sightings have now been added.
Unlike the painted lady, the peacock butterfly is not a migrant, instead they hibernate through the winter.
UK Butterflies: http://www.ukbutterflies.co.uk/index.php
Butterfly Conservation: http://www.butterfly-conservation.org/
Complete British Wildlife Photoguide (Collins - 1997)