First off thanks for your suggestions. I actually missed hostas, ferns and fatsia japonica (I love this plant) from my list. I was going to use rhubarb as a gunnera substitute as I don't think I've got enough room -what do you think?
There is already a 15 feet high cordyline palm in the garden and it currently looks very much out of place with the rest of the planting that was here when I inherited the garden.
The Miscanthus could be a good screen between the paths. Pheonix canariensis, although it has the exact look I'm after is not hardy enough unfortunately. I don't have a greenhouse and although I am going to heat a section of the polytunnel this winter it will be to keep my peppers alive through the winter (I'm fed up of starting them off from seed every year.
Having never grown cannas (I didn't say no to flowers btw - it's just that they are not my driving force in admiring a garden) I'm a bit wary of the amount of work to lift all of the rhizomes in autumn. I have a lot to do on my allotment plots at that time of year and the allotment always comes first. I think I've added another nice to have - low maintenance.
I've tried to grow Musa Basjoo for the last two years (in my previous garden) and it's died off in Winter even though I've tried to protect it - it can get very cold here. My site is quite open and there are only a couple of places sheltered to the wind. For this reason (until I had protection from established plants) I would be very hesitant to grow tree ferns either.
Hedichium is definitely added to the list. There are a lot of lilies in the garden already (they are taking over) and I intend to move most of them to around my pond on the allotment as the frogs love the thick foliage. Besides which my OH would not be impressed - she loves lilies (especially Zantedeschia aethiopica). I think I would need to see Rodgersia aesculifolia in the flesh as the images on google are not very consistent.
Aruncus dioicus would fit in very well and Crinum x powellii could be used too.
Can anyone think of ground cover for the edges of the paths that would disappear into the foliage?