That looks like Achillea - obviously I can't say which one it might be, or what colour the flowers might have been.

Aah there are some flowers still blooming elsewhere in the garden that are the same, they are bright pink. Is this a thug? It is giving a huge amount of shade.

It does spread, but I wouldn't call it a thug - unlike the native version, Pam, which is called 'Yarrow', has white flowers and is definitely a pain to remove.

it also has a look of pyrethrium [spelling] too. are the flowers large daisies or heads of tiny daisy type?

Not sure what the flowers from this plant (in the picture) but the other similar plant, which is pink, has small clusters of flowers. I'll add a pic.

then that makes it pretty certainly achillea as spritz suggested.