Now I know what it is (thanks to all those who responded), I looked it up in Wiki.
Interesting plant. Also, it says that some plants have been known to take 60 years to flower!I So planted for a baby at birth, they could be nearly pensioners before they see the flowers.
I asked because this looked similar to a plant which grows next door. It is about 12-14 feet high, so not the same. Many years ago, we cut this down for the elderly lady who lived there. It was growing in a silly place, and she wanted it gone. Obviously, we didn't get all the root out.
The house was later split into two flats, and this plant grows at the bottom and to one side of a flight of stairs from upstairs. It now 'belongs' to the upstairs flat after garden division. There have been a successioon of people living there, and the current tenants are 'garden-blank'. I have seen the chap cutting forsythia back with an ordinary pair of scissors! Plonker!
Maisie