ID large-leafed, yellow-flowered fast-growing bush help

Can anyone help identify this large-leafed bush for me. 

It flowers in spring I think (or maybe early summer) and has yellow flowers which kind of remind me of Magnolias. I've looked up those but couldn't find it.  They don't last long at all.

I'd like to id it as I want to control it and it seems to grow very quickly.

Any help much appreciated.