Confidence: I'm as sure as I can be.
Notes: Good clear images. If they'd extended, they would have had bluish tentacles; and the slime would be yellow or green. Limax maximus is very variable, but never yellow or green, and always with colourless slime and brownish tentacles. It's also fairly solitary as an adult, whereas the two yellow slug species are gregarious. Irish Yellow has a darker background, often green or brownish rather than yellow, and large pale blotches, whereas Yellow Slug Limacus flavus has quite fine pale speckles. Over most of Britain, Irish Yellow is a recent arrival, and seems to be increasing rapidly.