The Mystery Tree

Near the bottom of our garden, and right on the border with our neighbours, is a large tree.

As the leaves have developed, I'd hoped to be able to identify it, but I have to admit, I'm stumped.

I thought at first it was a lime tree - the leaves are a similar shape, but they are thicker and now there are some fluffy looking flowers to further confuse me.

So far, the websites I've checked haven't been able to help. Here are some pictures:



The tree itself is tall with quite a narrow canopy (although I think it may have been roughly cut back at some point.

As you can see, it's covered in ivy, so it's hard to see the bark, but I managed to get this close-up. It's slightly rough and a browny-grey colour.

Here are the leaves - these ones are not quite fully mature. They round out a little more and are quite large - roughly 3-4 inches across at the widest point.

Finally, these are the flowers (lots of which are dropping off right now). They are approx. 2-3 inches long. They have this cottony fluff and little black bits inside. Here's a close up:

Any ideas? I'd love to know what it is, so please add a comment if you can help.