This certainly appears to be an adult male Philaeus chrysops. The species is occasionally imported with produce from Mediterranean countries including for example tiles from Spain and Italy. It seems however that this species is unlikely to establish itself outdoors in Britain, at least currently, and there has been no evidence of any established populations (indeed to my knowledge no females have ever been recorded in this country, always only the spectacular male) - although the spider would be a nice addition to our fauna!
It would be worth knowing whether the lady had visited or had bought items originating from the Mediterranean recently.
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