Many thanks for all contributions.

I just tried breaking one of the 'seed' things in half and it is brittle and
dark brown all the way through. In short it does not look like there is
much life in it.

This tree is in a pot and is located in Central London and would have been
baked by last summers weather. I am wondering if this is in fact a
Paulowinia but one which produced seed pods with no seeds in. Maybe it
produced infertile seed pods because of the heat and drought conditions it
experienced last summer.

Phil