Yup; a gasteropod.  Makes me quite nostalgic, though to be honest I can't really remember what they tasted like.  My mum thought they were a waste of time, having been fed them regularly throughout her childhood (especially when the house got bombed and they had to live with relations on the coast who ate such things all the time) so we only had them very occasionally, when I was small.  My dad was a bit more keen, but they were more of a novelty for him... he wasn't an Eastender.