Iris ?

Look like Iris to me also. A nice surprise!

iris

Oh wow a very nice surprise although I've no idea where they came from! Aren't irises a rhizome plant?
Thank you for your help!

eilnan - they will have been there all the time. They don't self seed. Either the rhizomes were under the soil and had no leaves or you didn't notice them earlier because the leaves were shorter. They are evergreen here so you should be able to keep an eye on them now. Slugs love them.

Yes, iris grow from rhizomes. Most are spring-bloomers, though some newer varieties bloom in the fall also. (My limited experience is with bearded iris.)

I have a neighbor who, as soon as her iris have stopped blooming, cuts the leaves back to about 3" tall. I'm not sure how widespread that practice is, but perhaps you just bought the house recently, and the Previous Owners had cut the leaves back to the point that you didn't know there were any iris at all?

I'm fairly sure they haven't appeared above ground in the last 3 years so its a mystery! :-). Thanks for the slugs tip although they don't seem to have discovered them yet. Will wait and see and hopefully they'll bloom in spring. Can they be moved easily?

Could possibly be Iris domestica (blackberry lily) that got spread by birds.

Ah ok, thank you dave_in_nova. Do you know when they flower?

OP is in the UK (don't know why the zone has changed to 10) so unlikely to be blackberry lily. It's barely known here.

Hi
Yes I am from UK - don't know why but it keeps reverting back to zone 10 even though I change it - it can be very hard to see this when I am responding from my mobile. Thanks for your help.
Regards
Eileen

eilnan, IIRC, to make a permanent change in your zone field, you need to do it on your member page rather than when you make a post (even though you can make a temporary change here when posting).

Why they set it up that way -- what the advantage was supposed to be -- I don't know.

Great, thank you missingtheobvious! :-)

I had little small plants like this appear in my garden and thought they were some sort of mini iris, but it had a flower similar to a sedge.

eilnan's plants are not sedges. There's nothing else they could be, apart from Irises, given the location and appearance, other than Sisyrinchium striatum which is fairly unlikely, but possible.