Um, when you say climber, how tall is this plant? And what part of the world are you in?

It looks like a sycamore to me. They grow like mad and seed like crazy, which is why sycamore (and ash) trees are known as 'weeds of the forest'.

It certainly doesn't look like any climber I'm aware of, but see what others say.

Not a sycamore surely...

Isn't it a clematis? I've got one with leaves similar to this one.

Which variety is it, Landgirl, the one you've got I mean?

I've just been out to the garden to check if it's like my Clematis Montana leaf and it's very similar, so I'd say it's a Clematis too.

It might be, Cammomile, there's definitely a petiole visible in the picture which appears to be trying to curl around a leaf, but I've no idea which variety it could be...

In hindsight, I can't believe I thought this might be sycamore. On second viewing, it's nothing like one.

Senior moment plus... :((

Hi just looked at pic. Looks like my Broughton Bride clematis. Very pretty with hanging white flowers. Hope this helps.