Confidence: I'm as sure as I can be.
Notes: There has been some new work on Ornithogalum recently, resulting in some changes in nomenclature. Not entirely due, this time to DNA based taxonomy, but also due in part to some confused recording. So it would be good to get it right now. There are four species altogether but only two are at all common. O. pyrenaicum has rather smaller flowers (<28mm) in a long raceme and is a native found only in the South, about as far North as Huntingdonshire. The commoner plant is now O. umbellatum which has larger flowers in a corymb. Importantly there are two subspecies of which the distribution is not well known. The commonest is certainly subsp. campestre, the native version which tend to have fewer flowers (<12) and flowers up to 40mm. The introduced subsp. which needs to be looked for has 12-20 larger flowers, up to 60mm.