It's a houseplant

http://www.ehow.co.uk/way_5608417_yucca-elephantipes-plant-care.html?cr=1 hope this helps you as Bamboo said its an indoor plant, so you should bring it in doors.

I'm pretty sure you can grow them outside as well, they are considered as 'fairly hardy'. I have 3 in my garden and they have made it through last Winter without any protection. I would cover it over with a fleece tent in colder parts of the country. Here are some pictures of mine in my blog. The Yucca is on pictures 1, 2 ,3 and 6. It could be another variety?

I have a yucca in my garden too but its not this one.

Yucca elephantipes is a houseplant in Britain, Andrea - yours are other varieties.