Could you add a photo to your question, so we can check the ID, please? It would be very early for a Cordyline to flower.

Might be a Phormium, Landgirl - they're coming into flower in London now, but, as you say, not only is it early for a Cordyline, but they don't usually flower until they've got a good trunk on them. Bit early for Yucca yet too, though not impossible, so Norlands, please do post a photograph for ID purposes. None of these plants would just appear though - its possible there was a cordyline that got cut down and its regrown, that might explain what's happening, but hard to be certain without pictorial evidence.