I'd have a stab at Dracena marginata, But I havent seem such a swollen base before... a bit like the Beacarneas base, but the leaves seem wrong... probably shouldn't post when I know so little about house plants ;)

I've seen what look like much smaller versions for sale in Focus.
Sorry for the lack of help, but now I can keep an eye on this through my homepage.

Hi there Guest,look up ponytail palm,aka elephant foot,bottle palm. Though it is not a true palm.Beaucarnia recurvata is a native of Mexico.It should be treated as a cacti as it stores it's water.
If you've had it for 15 years you know how to look after it anyway,lol. A lovely healthy looking plant :)

Thank you to sg maintenance, Meanie and Aster. I'm sure now that it is the Beaucarnia. It does get treated as a cacti and I'm surprised that it has hardly grown. Thank you again for your replies.Koicarp xx

It will grow a little faster if it gets a little sun, and light feeding a couple times a year--any good plant food, 1/3 recommended strength.