It looks like a Datura, to me. Was the spiny capsule preceded by a big white or purplish, night-blooming flower?

I agree with Tug, it's a Datura stramonium.

This plant made interesting reading on http://medplant.nmsu.edu/datura.html

Thanks everyone. I looked it up on a couple of sites and it looks a bit of a nasty plant. Will have to get rid of it. Can't sfford to let it seed as I keep livestock.
Thanks again
Richard