Probably a hybrid. You do get occasional white native bluebells, but the bells are more slender and taper to a 'waist' before the petal tips curl strongly upwards. Those flowers look altogether too hefty, though they are only on one side of the stem, a native trait.
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https://gardening.which.co.uk/hc/en-gb/articles/360000144769-English-Spanish-and-hybrid-bluebells