Flowering plant ID, please.

I've had this tall, clumping plant in my back garden for 2 years now. I thought I'd ID'ed it last year but can't find it in my named plants list.

I seem to remember that it produces largish daisy-like flowers in small groups at the top of the plant. It's much more erect and robust than ox-eye daisy, and grows over a metre tall. Any help identifying will be much appreciated.