Thanks for your replies.
Unfortunately it's not a recent find. It was used for years by my grandmother as a doorstop, and I have no idea where it came from before that.
It would just be really nice to pin down what species it's from.
Actually, after looking at it even more it seems too white to be old. It could be off a modern day elephant. Do you have a microscope? If you do you would be able to put it under the microscope and it you can see grains of sand or something like that it is a subfossil. Woolly mammoth fossils are not fossils-they are usually sub-fossils. Here is one of many mammoth teeth in my collection. It looks identical, appart from it is darkest in colour. For your tooth, I can't tell if it is from a mammoth, a mastodon or an elephant, but I can garuntee it is off something related to an elephant, if not an elephant.
It looks like an Asian Elephant tooth to me. It is definately not a Mastadon tooth, they look totally different.
There is an article on here that might help.