What is its scientific or Latin name? I can't find it under Bird Bill.

I imagine you're talking about a variety of Hemerocallis, the day lily. They're alright I suppose - very attractive flowers, each one lasts a day, lots of sword shaped green leaves, lots of people love 'em. As you can tell, I'm not that keen, lol, but that's just personal preference.

Hi, welcome to GoY, bird bill dayflower, proper name, Commelina dianthifolia, genus of over 100 species, sold by some nurseries as hardy, an able to stand temps down to minus 8c, in fact they are at best frost hardy, mostly frost tender, are summer flowering, and flower in the first year from seed, and like Dahlia's form tubers, native to warmer parts of north america, ie, arizona, colorado,new mexico, texas and northern mexico.
You don't say where you are in the world, but if you're in the UK, I wouldn't try to grow them permanently planted in the flowerbed, Derek.

That's disappointing. There is a hardy little spring flowering plant about the same size that has little blue flowers and leaves like very miniature irises that might compensate you a bit. Because my memory for names lets me down all the time these days I can't tell you the name but I could send you a bit if you sent me a Private Message (click on my avatar to reach my home page and you'll see the option on there)

Thank you all for your comments . I haven't been on this website since posting , so sorry for belated thanks. I love the bright blue of this flower which is indeed Commelina Dianthifolia but they are quite fragile and the foxes have knocked all the blooms off . So I will buy Salvia patens Cambridge blue (very similar colour) but much larger and tougher. I live in Orpington Kent .