A spectacular butterfly from the continent could be attempting to colonise the UK, experts said after a number emerged on the south coast.

A dozen adult continental swallowtail butterflies have been seen across Sussex in the past few weeks after wintering in the UK, wildlife charity Butterfly Conservation said.

Last year's hot summer led to the the largest invasion of continental swallowtails since 1945, with adults laying eggs in a number of gardens in Hastings, Eastbourne and Chichester, while butterflies were also seen in Suffolk, Kent, Hampshire and Dorset.

The butterfly - which resembles a species Britons would be more likely to see in a tropical butterfly house, with its striking black and yellow markings and a streamer-shaped tail - finds it difficult to survive winter in the UK's relatively cold climate.

But the emergence of adults from pupae in recent weeks suggests its breeding attempts last year were successful, with the mild winter likely to have been a factor in helping them survive.

The UK already has a subspecies of swallowtail, the country's largest species of butterfly but smaller and darker than its continental cousin, which is restricted to the Norfolk Broads.

With a warming climate the continental swallowtail could become a UK resident in the near future, Butterfly Conservation said.

Michael Blencowe, from Butterfly Conservation's Sussex branch who has been monitoring the butterflies since they arrived last summer, said: "So far there have been 12 sightings of swallowtails in Sussex this spring.

"Six of these have been seen to emerge from pupae we were monitoring; others have been seen in Peacehaven, Chichester, Chanctonbury Ring and Horsham.

"There are still more to emerge and no doubt many other swallowtails that we don't know about are roaming the country, so there has never been a more exciting time to head out looking for butterflies.

"This current invasion could be the start of the colonisation of southern England by the swallowtail. In 20 years this butterfly could be a regular visitor to our gardens."

Butterfly Conservation is urging members of the public who see swallowtails to send details of sightings to www.sussex-butterflies.org.uk