They do look like Eryngium planum leaves, but could be another variety. Just let them grow on, see what they produce in the way of flowers.

Thanks, will do😊

as you have lifted them from the garden they will 'sit' for a while as they re establish new roots. then they will take off in the pots. They do look like E planumum and these are happy in free draining soil. they are sea hollies and therefore thrive in sandy soils.

Thanks Seaburn, I've had repeated problems in a strip by the East facing fence. It's only a small area but nothing thrives there & all space is at a premium in my tiny garden. I probably need to just get stuck in, go a fork deep, remove the rocks then make a raised box to fill with compost.
The two eryngia that survived are in large pots, gritty compost under cover so the only water they get is trickled down from the peppers on the shelf above. They seem to like it there but they'll get too tall eventually