They look like elms to me - they could have grown from the roots of elms that died of Dutch elm disease years ago - the roots often throw up suckers.
People got very excited when the first young trees grew from suckers following the loss of most of our elms, but unfortunately once they get to a certain size they too succumb to the Dutch Elm disease which is spread by a beetle.
Apparently the beetles aren't interested in the sapling size trees, but once they get bigger the beetles bore into them and they're infected by the fungus spread by th beetle. I really miss the huge English Elms that were such an important part of the countryside when I was a child.
More information here http://en.wikipedia.org/wiki/Dutch_elm_disease