I've just looked at my V. bonariensis. Yes, as you say @B3, the stems are angular, plus the leaves have an almost papery texture like mint - the leaves in the 4th photo here look a bit leathery with a blue tinge (V.B leaves are a fresher green).
This is centaurea just now in my garden. I'm no longer convinced now that it is this, but there are similarities, though this is slightly hairy rather than furry!
Thank you so much for the comments - I realise my photos aren't great! I'd recognise verbena bonariensis, so a leucanthemum seems much more likely. The person who's garden it is told me it had blue flowers, and I only know of white flowered types, but maybe they got confused. I think the other is more likely the centaurea - again, I think I'd recognise the stachys. as for the shrub - we'll have to leave it until spring and see again when it grows some leaves. Thank you!
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@Busy-Lizzie I've sent you a pm.