It's about 5" high and has slightly bluey green foliage and the emerging shoots looks like a little like Solomon's Seal, but narrower.
There are no leaves at all at the base of the stem and the flowers hang down, emerging from the leaves.
It's growing in shade under a shrub. The flowers are a subtle yellow with green near the stem.
I've just asked my neighbour and she thinks the previous occupant planted it, which means a: I'm not going loopy by forgetting I've planted it, and b: that it's probably quite unusual.
Can anyone help identify it?
Postscript - it's been identified as Uvularia Grandiflora by @BensBotanics on twitter, his website is here
Thanks Ben :-)