It looks a bit like a species of buddlia. If it's what I'm thinking of, I had one myself and it took a strong bloke an age to dig it all up. I agree that it spreads and sends up little seedlings. However, we seem to have got rid of ours now that the roots have been excavated. If it's not that then I apologise!

Sorry - I meant to say a type of buddleia or spirea!

Thankyou looks like I better get digging

Did you cut it down before spraying ? If you used a glyphosate weedkiller that will be why it didn't work. You need to spray it as it is, as it works by absorbing the stuff through the leaves. (its not a buddleia or a spirea, sorry Jane Susan)Sure I ought to know but it won't come...

It's Spiraea douglasii :)
I had one in my previous garden but try as I might I just couldn't kill it.

Thankyou both ill keep digging it up & hopefully it will go

Good luck ! :)

?

Well! I thought spirea at first but then thought most spireas had flat shaped flower heads and that put me off.
Sorry!

Thankyou

is it a shrub? if not are the leaves scented? if scented then it could be one of the mint family.