The usual method with phormium is to divide the clump in spring. The RHS says it can be grown from seed - it could be a long job but satisfying if you achieve anything of any size.

As to the method of propagating the plant in the picture - I was going to say try taking cuttings, then I realised it was two different plants - the foliage being nothing to do with the flowers.

Any seeds you collect from this plant, even if you got them to grow, may not be true to type, in other words, you're likely to get plain green or plain purple plants. You're probably best off buying a replacement if this one's got too big, but this time, pick one of the smaller varieties, those that only get about 4 feet, such as P. Cream Delight or P. Dazzler (3 feet). Best planted in spring though, not autumn.

I grew some from seed, yes it was easy and 7 yrs later it flowered.

Thanks for the info all. I think I leave the growing of the seeds seeing I may not flower for 7yrs, so I'll just dig it up & take the plant to the tip, Mmmm! I could offer it on Streetlife or Freecycle :o))

My husband Barry has just dug the plant up & I found the label..... It name was a Phormiim but was a Cookianum Duet so you weren't far off. I will add a Blog on how he got it out. Xx