A butterfly classed as extinct in the UK for more than 30 years has been seen at sites across southern England.

Once found across England and Wales, the large tortoiseshell was last recorded as a resident breeding species in the UK in the 1980s.

Adults primarily lay their eggs on elm trees and the population crash has been linked to the spread of Dutch elm disease across Europe in the 20th century.

Although there have been rare sightings over the years since, they are now becoming increasingly common.

The charity Butterfly Conservation has said that if it were to update its official endangered species list tomorrow, it would probably class the large tortoiseshell as no longer extinct after nature lovers captured photographs of large tortoiseshells in Kent, Hampshire, Sussex, Dorset, Cornwall and the Isle of Wight over the past month.

I wondered if any had been seen this year in Surrey. Bill Downey, chair of Butterfly Conservation’s Surrey & South West London Branch, told me the answer is no. However, Bill said there has been a sighting in Richmond Park: close, but not actually in Surrey.

The large tortoiseshell is a big, colourful butterfly with orange, black and blue wings. It is closely related to the small tortoiseshell but has different markings.

I told Bill of my dim recollection of seeing both large tortoiseshells and the common small tortoiseshells in the late 1960s as a boy growing up on the outskirts of Peterborough. But with only a children’s general encyclopaedia as my guide, I differentiated them only by size.

Bill advised me: “I think it much more likely you were seeing small tortoiseshells. Large tortoiseshells have always been extremely rare in the UK. I was born in 1953 and have never seen one.”

Can we look forward to seeing them in Surrey – and often? Bill said: “The large tortoiseshell sightings have mostly been in coastal areas and I think that is where they will probably remain for the time being.

“We would of course love to have all our native wildlife and butterflies back with us, but I’m afraid it is wishful thinking.”

Butterfly lovers have reported sightings of individual large tortoiseshells over the decades, but there has never been evidence of a stable breeding population, which would allow ecologists to classify it as a “resident species”.

However, in recent years there has been significant growth in the large tortoiseshell population in the Netherlands, and ecologists now think an increasing number might be flying across the sea to England.

The large tortoiseshell overwinters as an adult and emerges from hibernation on the first warm days of spring. This year's first reported sighting of large tortoiseshell was on the Isle of Wight on 24 February.

Members of the public reported at least 20 more sightings on the Isle of Wight, in Kent and Hampshire, and Butterfly Conservation’s Sussex Branch members have reported a string of sightings in their county.

Butterfly Conservation head of science Professor Richard Fox commented: "This is great news about a beautiful and charismatic butterfly.

"When a new species colonises, there is a period of uncertainty: many species that colonise take off and become common but some remain highly localised and can even then be lost; at the moment, for large tortoiseshell, we're in that ‘wait-and-see phase’."

If you see a large tortoiseshell please let me know, and try to take pictures: this evidence will assist Butterfly Conservation track its UK population. Hope to hear from you!