Although it is technically a non-native species, as it was almost certainly brought to Britain by the Romans, Helix pomatia (the edible or Roman snail) is nonetheless protected by the Wildlife and Countryside Act (1981), and in England it is an offence to sell, collect, kill or injure this species. That’s an unusual situation for an alien animal or plant in this country, and I’m struggling to think of another example – are there any?
Regardless of its status, the large shells of the Roman snail (several times bigger than the common garden snail Cornu aspersum when fully grown) form a beautiful spiral for today’s Spiral Sunday posting.
Thanks to Dr Tim Astrop for allowing me to photograph this dead specimen.
Prof. Jeff Ollerton - ecological scientist and author 
Probable early introductions
Brown hare (different partial protection)
More recent reintroductions
Capercaillie
Large blue
White tailed eagle
We will probably never know how they got here
Starlet sea anemone
Ivell’s sea anemone
Medicinal leech
Some beetles
Some moths
Trembling sea-mat
Lagoon sandworm
Small alison
Field eryngo
Many other plants
And of course most species have been moved by people within the UK and are protected wherever they have ended up.
Thanks Matt, that’s really useful. Personally I wouldn’t count re-introductions in the same way, but even so it’s a lot more species that I’d thought.