Statice. You can dry them and put them in arrangements.

Thank you

Used to be labelled Statice, now that's the old name - its official handle is Limonium sinuatum. Great plant, easy to grow. If you like these sort of 'ready dried' everlasting type flowers, try also Xerocrhysum bracteatum (what a mouthful, used to be called Helichrysum) common name strawflower. I've still got the heads as pot pourri of plants I grew oh, must be easily 35 years ago...not been kept in sun though, or they'd have faded badly by now! Pics in the link below
https://www.swallowtailgardenseeds.com/annuals/strawflower.html

Thanks again, I did wonder if there was a reason why the plants at Harlow Carr were all grown around the raspberries, do you think they could be some sort of companion plant?

Not so far as I know, but statice is only an annual, so maybe they sow annuals, clearing them in autumn to allow new raspberry shoots to appear. By the following spring early summer, they can plant new annuals without interfering with any new raspberry growth (being able to see where it is), so that might be why.

Sounds a good explanation to me. Thanks :-)