Lena, it's a Yucca. If the tips are sharp and painful, it is probably Yucca aloifolia (not a good houseplant unless you have more eyes than you need!), if the tips of the leaves are soft, it is likely Yucca elephantipes (aka spineless yucca) which is the most common one.
A trowel in the hand is worth a thousand lost under a bush.
I always put mine outside in the summer but it's not properly hardy over the winter where I am (Essex). I got fed up with mine when it reached the roof of the conservatory and so I left it out over the winter. It died back completely and I assumed it was dead but then it grew back from the bottom so I split off the new growth and now have a completely new, manageably sized plant.
Ooh, thanks Singing Gardener. The last couple of winters have been quite mild down here in Cornwall. There are some similar looking ones that people have growing in their gardens nearby, so it might do ok outdoors over the winter.
Thanks for the advice also Hostafan. I'll make sure I choose a spot in the garden that doesn't get too much full sun
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Lena, it's a Yucca. If the tips are sharp and painful, it is probably Yucca aloifolia (not a good houseplant unless you have more eyes than you need!), if the tips of the leaves are soft, it is likely Yucca elephantipes (aka spineless yucca) which is the most common one.
Thanks Bob
Yes, the ends of the leaves are sharp so it's the aloifolia one. Fortunately for me I'm only 5 ft 4 and they are above eye level for me 
That one is also known as 'Spanish dagger'!
I can see why!
I've just googled it and it says it's hardy so I think I might move it outdoors in the summer
I always put mine outside in the summer but it's not properly hardy over the winter where I am (Essex). I got fed up with mine when it reached the roof of the conservatory and so I left it out over the winter. It died back completely and I assumed it was dead but then it grew back from the bottom so I split off the new growth and now have a completely new, manageably sized plant.
Watch out for leaf scorch if you put them outside in full sun.
Ooh, thanks Singing Gardener. The last couple of winters have been quite mild down here in Cornwall. There are some similar looking ones that people have growing in their gardens nearby, so it might do ok outdoors over the winter.
Thanks for the advice also Hostafan. I'll make sure I choose a spot in the garden that doesn't get too much full sun