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I cannot tell from this picture if this is Cepaea hortensis.
The animal is a juvenile with scarcely 4 whorls instead of the 4.5-5 of the adult.
I suspect the white band seen near the mouth of the shell is the pigmentation of the mantle showing through the translucent shell. To be sure of Cepaea hortensis rather then C. nemoralis the pigmentation of the thickened inner lip of the shell of the adult is required. As has been pointed out at http://www.ispot.org.uk/node/6763 C. nemoralis with a white lip does occur. Measurements of the shell dimensions will distinguish the two species (C. nemoralis is consistently larger). For juveniles see comments in John G. Evans Land snails in archaeology; with special reference to the British Isles. London, New York, Seminar Press, 1972. xii, 436 p. illus. 24 cm. ISBN: 0128295503.
Also love dart and details of genitalia are different but require dissection.
Thank you very much. Now I have a better idea of what I'm looking out for.
Lat/Lng: 51.0845, 0.0316
OS grid ref: TQ423336