Kew Gardens wild flower mix lily?

Last year we were graced by the appearance of this wild lily in the corner of our Rhubarb patch in the allotments. Its source was a mystery. There were two possible explanations: it had arrived curtesy of the floods that the allotments are subject too; or it had grown from a seed included in the Kew Gardens’ wild flower mix that had been sown in the allotment borders the previous season. Well it certainly like it here since whereas we had one flower spike last year, this year we have four.