Hi, I wonder if you could help me. Im afraid I'm not much of a gardener and I require some advice on the type of tree/plant in the attached photo and i also would be grateful on ideas of how to prune/cut it back. I like the plant so don't want to remove it but now it's taking over. My past efforts at pruning invariably end up with dead plants.

Hi AlistairC,
Your plant looks like a Yucca to me. If it has extremely sharp tips, it might be Adam's Needle (Yucca filamentosa) or Spanish Bayonet (Yucca aloifolia)

There is also a variety that has softer tips: Spineless Yucca (Yucca gigantea)